摘要:

Vascular plants have respiring tissues which are perfused by the transpiration stream, allowing solubilization of respiratory CO2in the xylem sap. The transpiration stream could provide a conduit for the internal delivery of respiratory CO2to leaves. Trees have large amounts of respiring tissues in the root systems and stems, and may have elevated levels of CO2in the xylem sap which could be delivered to and refixed by the leaves. Xylem sap from the shoots of threePopulus deltoidestrees had mean dissolved inorganic carbon concentrations (CO2+H2CO3+HCO−3) ranging from 0. 5 to 0. 9 mM. When excised leaves were allowed to transpire 1 mM[14C]NaHCO3, 99. 6% of the label was fixed in the light. Seventy‐seven percent of the label was fixed in major veins and the remainder was fixed in the minor veins. Autoradiography confirmed that label was confined to the vasculature. In the dark, approximately 80% of the transpired label escaped the leaf, the remainder was fixed in the major veins, slightly elevating dark respiration measurements. This indicates that the vascular tissue inP. deltoidesleaves is supplied with a carbon source distinct from the atmospheric source fixed by interveinal lamina. However, the contribution of CO2delivered to the leaves in the transpiration stream and fixed in the veins was only 0. 5% of atmospheric CO2uptake. In the light 90% of the label was found in sugar, starch and protein, a pattern similar to that found for atmospheric uptake of[14C]CO2. Compared with leaves labelled in the light, leaves labelled in the dark had more label in organic acid, amino acid and protein and less label in sugar and starch. After a 5‐s pulse the majority of the label fed to petioles in both the light and the dark was found in malate. The majority of the label was found in malate at 120 s in the dark; only 2% of the label was found in phosphorylated compounds at 120 s. The proportion of label found in phosphorylated compounds increased from 17% at 5 s to 80% at 120 s in the light. This suggests that CO2delivered to leaves in the light via the transpiration stream is fixed in the veins, a small portion through dark fixation into malate, the remainder by C‐3 photosy

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb00150.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The ability of legume nodules to regulate their permeability to gas diffusion has been attributed to physiological control over the size and distribution of gas‐filed intercellular spaces within the nodule cortex. To examine the size and distribution of intercellular spaces and to determine whether they were filled with gas (high diffusion permeability) or liquid (low diffusion permeability), whole nodules were frozen in liquid nitrogen slush (‐210°C), and then either cryo‐fractured or cryo‐planed before being examined by cold‐stage scanning electron microscopy (SEM). The cryo‐planed tissue was found to have many advantages over cryo‐fractured nodules in providing images which were easier to interpret and quantify. Intercellular spaces throughout the nodule were examined in both tangential and medial planed faces. Since no differences were observed between views in either the size or shape of the open intercellular spaces, it was concluded that the intercellular spaces of nodules were not radially oriented as assumed in many mathematical models of gas diffusion. The inner cortex region in the nodules had the smallest intercellular spaces compared to other zones, and less than 10% of the intercellular spaces were occluded with any type of material in the central zone regions. Vacuum infiltration of nodules with salt solutions and subsequent cryo‐planing for SEM examination showed that open and water‐filled intercellular spaces could be differentiated. The potential is discussed for using this method to study the mechanism of diffusion barrier regulation

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb00151.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The effect of seed‐tuber age on the ability of tuber tissue to synthesize protein during sprouting was examined. As seed‐tuber age advanced from 4 to 32 months (at 4°C, 95% relative humidity), soluble protein concentration of tubers decreased linearly, with a concomitant increase in free amino acid concentration. The age‐induced loss of tuber protein may thus be due to increased proteolysis, decreased protein synthesis, or both. Five‐ and 17‐month‐old seed‐tubers were compared for their ability to incorporate radiolabeled amino acids into soluble protein at equivalent stages of sprout development. Tuber respiration was profiled through each sprouting stage to characterize the physiological status of the seed‐tubers prior to incorporation studies. Five‐month‐old seed‐tubers maintained a constant rate of respiration during sprouting. In contrast, respiration of 17‐month‐old tubers increased as sprout dry matter increased, resulting in a 2‐ to 3‐fold greater respiratory rate from the older tubers, relative to the younger tubers, at similar stages of sprout development. Prior to sprouting, the rate of incorporation of amino acids into trichloroacetic acid‐precipitable protein of tissue from 5‐month‐old tubers was 2. 9‐fold higher than that from 17‐month‐old tubers. More importantly, protein‐synthetic capacity of tissue from younger tubers increased about 1. 7‐fold during sprout development. Despite the higher respiratory activity and faster total sprout dry matter accumulation from older seed‐tubers, protein synthesis remained at a low and constant level through all stages of sprouting. Protein‐synthetic capacity thus declines with advancing tuber age, and this may contribute to reduced growth potential during the latter stages of establishment by affecting the ability of seed‐tubers to synthesize enzymes involved in mobilization and

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb00152.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Twenty one‐day‐oldPhaseolus vulgaris‘Saxa’plants were cultured in a growth chamber and the plants supplied with either a complete or a Mg‐free nutrient solution. From 6 days after transfer to the Mg‐free solution, the rate of increase of the area of the second trifoliate leaf was considerably reduced; by day 11 the sucrose concentration in the first trifoliate leaf had increased 6. 2‐fold at the end of the dark period and 4. 6‐fold after the light period as compared with the control plants. Corresponding starch concentrations increased 6. 6‐fold and 2. 9‐fold respectively. After days 5 to 6 the assimilation rates declined in the first trifoliate leaf of the plants showing deficiency, in comparison with the plants fully supplied with nutrients; respiration increased during darkness. The reduction in net assimilation rate was to a great extent reversible after resupply of magnesium.The reduction of magnesium concentration in the deficient plants was much more marked in the expanding leaves than in the mature primary leaves and roots. Sucrose and starch accumulation did not occur when the first trifoliate leaf was partially shaded, although magnesium concentration, as in the unshaded leaves, was reduced to 13% of that of the control plants. The consequences of magnesium deficiency in the expanding first trifoliate leaf are discussed in terms of the possibility

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb00153.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Oxalis regnelliiMig. is a trifoliate plant, and the three leaflets usually show synchronized up and down movements with a circadian period of 26–27 h. The three leaflets can also perform desynchronized ultradian oscillations, and we report on such rhythms under different conditions. A study of the occurrence of ultradian leaf movement rhythms as a function of irradiance is presented. At an irradiance of approximately 1 μW cm−2, the occurrence was maximal and ca 30%. The periods varied from 5 to 15 h. Four other cases of ultradian rhythms in different conditions are also presented. In one case spontaneous ultradian rhythms occurred, and in another, two of the leaflets showed ultradian rhythms when the third leaflet had received a light pulse. In two more cases, the three leaflets on a leaf were separated by physical cuts along the petiole between the pulvini; in both cases the period was approximately 5 h. Possible mechanisms to explain the ultradian rhythms inOxalis regnelliare discu

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb00154.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The composition and positional distribution of fatty acids in the polar lipids from 4 strains ofChlorelladiffering in chilling susceptibility and frost hardiness were analyzed by enzymatic hydrolysis and gas‐liquid chromatography. Analysis of the polar lipids from chilling‐sensitive, chilling‐resistant and chilling‐sensitive revertant strains ofChlorella ellipsoideaIAM C‐102 showed that the sum of palmitic andtrans‐3‐hexadecenoic acid in phosphatidylglycerol (PG) is about 60% for the sensitive strains and 53% for the resistant strain. The sum of dipalmitoyl and 1‐palmitoyl‐2‐(trans‐3‐hexadecenoyl) PG as estimated from the positional distribution of their fatty acids, is about 10% in the case of each of the three strains. The contents of unsaturated fatty acids in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were higher in the resistant than in the sensitive strain. This suggests that unsaturation of fatty acids in not only PG but also PC and PE is involved in chilling sensitivity ofChlorella. On the other hand, lipid changes during the development of frost hardiness ofC. ellipsoideaIAM C‐27, a frost hardy strain, were examined. The results showed that fatty acids in most lipid classes are unsaturated in the hardening process but their degree of unsaturation is not greatly different from that of the chilling‐resistant strain, suggesting that not only unsaturation of fatty acids in lipids but also other factors are necessary for the dev

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb00155.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Two petunia (Petunia hybridaL.) lines, differing in their flower longevity, were studied, Similar tendencies were found in the changes of corolla fresh weight, electrolyte leakage and membrane microviscosity over the life spans of the two lines. Ethylene production by flowers of the two lines showed a similar pattern, peaking at 3 nl flower−1h−1. However, in flowers of the short‐lived line, ethylene production peaked at 6 days of age, but in the long‐lived line, the peak appeared at 10 days of age. A large difference was found in the responsiveness of the flower to ethylene, Flowers of the short‐lived line responded to a similar ethylene by immediate wilting, while those of the long‐lived line responded to a similar ethylene treatment only after two days. Differences in sensitivity to ethylene were also, observed when the flowers were treated continuosly with (aminooxy)acetic acid, which blocks ethylene synthesis. Flowers of both lines responded to ethylene treatment by increased ethylene production to a similar rate. Differential sensitivity to ethylene, independent of ethylene production, seemingly governs flower longevity in the two petunia li

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb00156.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Mitochondria isolated from cotyledons of dark‐grown cucumber (Cucumber sativusL., cv. Shimotsuki‐Aonaga) seedlings after illumination with continuous far‐red light showed an increased capacity for oxidation of malate or α‐ketoglutarate, as compared with those from cotyledons of non‐illuminated seedlings. This increase is supposed to be caused by phytochrome action (high irradiance response). Exogenous NAD+had no effect on the rate of the oxidation of α‐ketoglutarate or malate by mitochondria isolated from far‐red light‐treated cotyledons, but it enhanced the oxidation rate of mitochondria from control cotyledons to the level of mitochondria from light‐treated ones. The NAD (NAD++ NADH) content was higher in mitochondria isolated from continuously far‐red light‐treated cotyledons than in mitochondria from controls. The NAD content was also increased by the treatment with a red light pulse and this response was reversed by a subsequent far‐red light pulse. It is proposed that phytochrome controls respiratory activities of cucumber mitochondria by changing the size of the NAD

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb00157.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The accumulation of glycoalkaloids that normally takes place in aerobically incubated potato (Solanum tuberosumL.) tuber discs has been found to be inhibited by the ethylene‐releasing substance ethephon. Using ethephon and the ethylene action inhibitor norborna‐2,5‐diene, the effect of ethylene on the synthesis of sterols and glycoalkaloids, which partly share their biosynthetic pathway, was investigated.Control discs showed incorporation of (2‐14C)mevalonic acid into free sterols, steryl esters, steryl glycosides and acylated steryl glycosides at 24 h, thereafter the radioactivity decreased in free sterols and steryl esters concomitant with the appearance of radioactivity in glycoalkaloids. Discs with ethephon additions contained more radioactivity in all sterol classes at all time‐points, but no glycoalkaloids were formed.The enzyme S‐adenosyl‐l‐methionine:sterol C24 methyltransferase (SMT, EC 2. 1. 1. 41), located at one presumed branching point in the sterol and glycoalkaloid pathway, was characterized and found to exhibit similar characteristics as in other plants, but a lower specific activity. The activity of SMT increased in ageing tuber discs and this increase was further stimulated by ethephon, but inhibited by norborna‐2,5‐diene. The activity of the glycoalkaloid‐specific enzyme UDP‐glucose:solanidine glucosyltransferase (EC 2. 4. 1) also increased after slicing, but here ethephon additions counteracted the induction. The activity of the sterol‐specific UDP‐glucose:sterol glucosyltransferase (EC 2. 4. 1) was unaffected by either tuber slicing or ethephon additions.The results indicate that ethylene stimulates sterol synthesis in wounded potato discs, and that the wound‐induction of

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb00158.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The recessive dwarfing alleles of rye (Secale cerealeL.),ct1andct2, caused a 35–55% reduction in the length of leaf 2 compared with corresponding tall lines grown at both 10°C and 20°C. The dwarf lines were 45–50% as responsive to applied GA3as the tall lines at 20°C but the absolute GA‐responsiveness of the dwarfs was greater at 10°C than at 20°C. There was no significant difference in the contents of GA19, GA20, GA29, GA1, GA3and GA8in the leaf extension zone of tall and dwarf seedlings grown at 20°C. It was concluded that the mechanism whereby GA homeostasis is maintained is functional in both tall and dwarf lines despite marked differences in leaf extension rate. The recessive rye mutations may cause loss of function late in the GA‐cell elongation pathway or, alternatively, indirectly affect GA‐responsiveness in vegetative tissues. The genetic and physiological evidence indicates thatct1andct2are unrelated to the GA‐insensitiveRhtgenes in hexa

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb00159.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY