摘要:

Soluble ADPglucose-α-glucan 4-α-glucosyltransferase (starch synthetase), ADPglucose pyrophosphorylase, UDPglucose pyrophosphorylase and phosphorylase were assayed in extracts from developing kernels of maize (Zea mays). Normal, waxy and amylose-extender maize at stages of development ranging from 8 days to 28 days after pollination were studied. Shrunken-4 maize at the 22-day stage was also studied. There is adequate activity of both ADPglucose pyrophosphorylase and starch synthetase at all stages of development to account for the synthesis of starch. Thus all starch could be synthesized via the ADPglucose pathway. High levels of UDPglucose pyrophosphorylase and of phosphorylase activities were also found at all stages of development. The possible role of phosphorylase in starch synthesis could not be discounted. The levels of phosphorylase, ADPglucose pyrophosphorylase, starch synthetase, and UDPglucose pyrophosphorylase activities in shrunken-4 kernels were about 20 to 40% of that found in normal maize kernels. It appears that the mutation in shrunken-4 affects the activities of more than one enzyme. The defective starch synthesis seen in this mutant could be due to the low activities of ADPglucose pyrophosphorylase and starch synthetase rather than the low activity of phosphorylas

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1973

数据来源: ASPB

摘要:

The effect of indoleacetic acid and 2,4-dichlorophenoxyacetic acid on the ripening of intact mature-green pears (Pyrus communisvar. Bartlett) was investigated using a vacuum infiltration technique.The effects of indoleacetic acid and 2,4-dichlorophenoxyacetic acid at concentrations of 0.01, 0.1, and 1.0 mmeach were studied on softening, degreening, and on ethylene and CO2evolution. Softening and degreening were inhibited increasingly in response to increased concentrations of indoleacetic acid. This inhibitory property was amplified by 2,4-dichlorophenoxyacetic acid at concentrations comparable to those of indoleacetic acid. Application of the auxins also prevented the climacteric rise in respiration, but stimulated ethylene synthesis. Despite the presence of elevated ethylene levels, the inhibitory auxin effect was predominant.It is proposed that endogenous auxins in fruit represent a resistance factor in ripening and must be inactivated before ripening can occur.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1973

数据来源: ASPB

摘要:

The effect of illumination on the incorporation of labeled precursors into RNA of dark-grown maize (Zea mays) leaves was studied using either32P-phosphate or double labeling with14C- and3H-uridine. In the dark, label was preferentially incorporated into etioplast ribosomal RNAs. Incorporation into this fraction and into lower molecular weight fractions was strongly and preferentially stimulated by light during the first 2 hours of illumination. The effect persisted after illumination was terminated. The possibility that light-induced alterations in plastid ribosomal RNA metabolism may not be required for chlorophyll accumulation in maize is discussed.Sucrose density gradient analyses of ribosomes and of extracted RNA did not reveal light-induced incorporation of label into messenger-like RNA associated with polyribosomes during brief illumination. However, newly produced RNA which seems to be neither ribosomal RNA nor transfer RNA is detectable after illumination for 2.5 hours or longer.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1973

数据来源: ASPB

摘要:

When the midribs of untreated traps ofDionaea muscipulaare frozen in liquid nitrogen after rapid closure, they contain significantly less ATP than those frozen before closure. Exogenous ATP causes a significant increase in the rate of mechanically stimulated trap closure. Illuminated traps close faster than those kept in the dark. The traps of plants placed in 100% O2close much faster than do air controls, while 100% CO2inhibits closure. It is concluded that ATP is probably the native source of potential energy for contraction of the trap's midrib, and that if the endogenous ATP titer is increased by oxidative phosphorylation or an exogenous source, the trap will close faster.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1973

数据来源: ASPB

摘要:

Wounding of single leaflets of young tomato (Lycopersicum esculentumvar. Bonnie Best) plants causes the release of a proteinase inhibitor inducing factor. This factor is rapidly transported throughout the plant where it causes accumulation of inhibitor I, a potent inhibitor of several serine proteinases from both animals and microorganisms. The wound-induced accumulation of inhibitor I is both light- and temperature-dependent. In total darkness no accumulation results from wounding. The accumulation exhibits a linear dependence upon light up to 300 foot candles. At 600 foot candles and above, the response is maximal. In light the wound response possesses an unusual temperature dependence with an optimum rate of accumulation near 36 C. Below 20 C no accumulation occurs. The over-all process contains two light- and temperature-dependent steps, one involving wounding and transport, the other involving accumulation.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1973

数据来源: ASPB

摘要:

Tyrosyl-, arginyl-, leucyl-, and phenylalanyl-tRNA synthetase activities were measured in extracts from three root sections of 3-day-old pea seedlings. The sections 0 to 2, 3 to 7, and 8 to 22 millimeters from the root tip were chosen to represent the regions of cell division, elongation, and maturation, respectively. The specific activity for each aminoacyl-tRNA synthetase was highest in the 0- to 2-millimeter section and lowest in the 8 to 22 millimeter section. The changes in specific activity between the sections, however, varied with the particular synthetase. Tyrosyl-tRNA synthetase from each section was fractionated into two activity regions on a diethylaminoethyl cellulose column. Approximately 10, 22, and 44% of the total tyrosyl-tRNA synthetase activity in the 0 to 2, 3 to 7, and 8- to 22-millimeter sections, respectively, were associated with the first tyrosyl-tRNA synthetase region; the remaining activity was located in the second tyrosyl-tRNA synthetase region. Only one activity region for arginyl-tRNA synthetase was detected by diethylaminoethyl cellulose column fractionation.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1973

数据来源: ASPB

摘要:

The ultrastructure of inner membrane-matrix mitochondria isolated from bean (Phaseolus vulgaris) shoots was examined in different metabolic states. Gross ultrastructural transformations analogous to the condensed-to-orthodox configurational changes reported in mammalian mitochondria are observed on transistion from nonrespiring to respiring metabolism. With the induction of oxidative phosphorylation, the particles remain in the orthodox configurational state. The reverse orthodox-to-condensed configurational changes observed in mammalian preparations does not occur. Optically monitored absorbancy studies with bean particles show a substrate-supported Pi-induced swelling under the same conditions that induce the condensed-to-orthodox ultrastructural transformation. The swelling is associated with the net uptake of K+and Pias well as a small Pi-induced respiratory stimulation. When phosphorylation is initiated with these swollen particles, the optically monitored volume remains unchanged. Thus a positive correlation exists between the ultrastructural configuration and the osmotic volume changes, which supports the conclusion that configurational changes reflect internal osmotic adjustments.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1973

数据来源: ASPB

摘要:

Diurnal changes in the vertical profiles of irradiance incident upon the adaxial leaf surface (I), stomatal resistance (rs), leaf water potential (ψ), osmotic potential (π), and turgor potential (P) were followed concurrently in crops of maize (Zea maysL. var. Pa 602A), sorghum (Sorghum bicolor[L.] Moench var. RS610), and tobacco (Nicotiana tabacumL. var. Havanna Seed 211) on several days in 1968 to 1970 when soil water potentials were high. In all three crops thers, measured with a ventilated diffusion porometer, theψ, measured with the pressure chamber, theπ, measured with a vapor pressure osmometer, and the calculatedP, decreased from sunrise to reach minimum values near midday and then increased again in the afternoon. The diurnal range of all the variables was greater for leaves in the upper canopy than for those in the lower canopy.Pwas observed to decrease with decreasingψ, but never became zero. Sorghum had a higherPat aψof, say−10 bars, than did maize, and maize had a higherPthan tobacco at the sameψ. Moreover, at the sameψthe upper leaves in all canopies had a higherPthan the lower leaves. When compared at high irradiances,rsdid not increase asψdeclined to−13,−15, and−10 bars or asPdeclined to 0.3, 3.5, and 1.2 bars in maize, sorghum, and tobacco, respectively. The relation betweenrsandIin the upper, nonsenescent leaves of all three crops fits a hyperbolic curve, but the response varied with species and leaf senescence. The adaxial and abaxial epidermises had the same response ofrstoIin maize and sorghum, whereas in tobacco the adaxial epidermis had a higherrsthan the abaxial epidermis at all values ofI. At equal values ofI, tobacco had the lowest leaf resistance (rl) and maize had the highestrl. Senescent maize leaves had nonfunctional stomata, whereas the lowermost sorghum leaves had higher stomatal resistances on average than

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1973

数据来源: ASPB

摘要:

The cotyledons and embryo axes of seeds ofPhaseolus vulgarisL. cv. Pinto contained 16% of the total calcium in the seed. The remaining 84% was in the testas. There was no evidence that calcium in testas was used in seedling growth or that calcium was leached from seedlings during growth.An external supply of calcium decreased the incidence of hypocotyl collapse (a severe symptom of calcium deficiency), increased the calcium content of all organs, and increased the dry weight of all organs except cotyledons. Light treatments decreased the incidence of hypocotyl collapse and increased the calcium content and dry weight of all organs except cotyledons and hypocotyls.White light was more effective than far red light for decreasing incidence of hypocotyl collapse. Usually the effects of white light and far red light on the calcium content and dry weight of organs were similar, and usually those of white light were quantitatively greater than those of far red light. It is suggested that the light-promoted effects were associated with photomorphogenesis and that differences in data obtained with white light and far red light could be associated with photosynthesis.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1973

数据来源: ASPB

摘要:

Phosphorus deficiency was induced in sugar beet plants (Beta vulgarisL. var. F5855441), cultured hydroponically under standardized environmental conditions, by removal of phosphorus from the nutrient supply at the ten leaf stage 28 days after germination. CO2and water vapor exchange rates of individual attached leaves were determined at intervals after P cutoff. Leaves grown with an adequate nutrient supply attained net rates of photosynthetic CO2fixation of 125 ng CO2cm−2sec−1at saturating irradiance, 25 C, and an ambient CO2concentration of about 250μl l−1. After P cutoff, leaf phosphorus concentrations decreased as did net rates of photosynthetic CO2uptake, photorespiratory evolution of CO2into CO2-free air, and dark respiration, so that 30 days after cutoff these rates were about one-third of the control rates. The decrease in photosynthetic rates during the first 15 days after cutoff was associated with increased mesophyll resistance (rm) which increased from 2.4 to 4.9 sec cm−1, while from 15 to 30 days there was an increase in leaf (mainly stomatal) diffusion resistance (rl′) from 0.3 to 0.9 sec cm−1, as well as further increases inrmto 8.5 sec cm−1. Leaf diffusion resistance (rl′) was increased greatly by low P at low but not at high irradiance,rl′for plants at low P reaching values as

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1973

数据来源: ASPB