摘要:

The nacreous walls of sieve elements occur in seagrasses in all three genera of the family Zosteraceae and the genusHaloduleof the family Cymodoceaceae but are absent from another eight seagrass genera belonging to the families Hydrocharitaceae, Cymodoceaceae, and Posidoniaceae. They occur in leaf blades, leaf sheaths, rhizomes, and erect stems but are not present in root tissues. The nacreous wall is uneven along the inner limits reflecting irregular thickness. The wall consists of hemicellulose or pectin and cellulose, but no protein, lignin, or lipid. Ultrastructurally, the wall contains parallel microfibrils or loose fibrils embedded in an amorphous matrix. Open pores occur in sieve plates and branching plasmodesmata are present in enlarged sieve areas. Mitochondria, endoplasmic reticulum, and plastids are also present in these sieve elements.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07854.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Boron deprivation has multiple effects upon root growth within 6 hr after this essential micronutrient is withheld. Root elongation is inhibited and this response has been attributed to a cessation of mitosis and DNA synthesis. Our preliminary results using an autoradiographic analysis of sunflower roots labeled with [3H]‐thymidine demonstrated no difference in label distribution between +/‐B root tips. We found that mitosis in inhibited in ‐B roots but does not completely cease. Scintillation counting of whole root tips shows that boron‐deficient roots up to 72 hr of treatment incorporate radioactive label at a level comparable to that of the controls. Because mitosis and presumably DNA synthesis are affected by prolonged boron deficiency, these results may be brought about by a change in membrane integrity or permeability. We propose that effects of boron deprivation on DNA synthesis and mitosis in sunflower are secondary and that primary events involve alterations in cellular membranes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07855.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Foliar surfaces of nine pleurothallid orchids (Cryptophoranthus lepidotusL. O. Wms.,Octomeriasp.,Pleurothallis pidaxLuer,P. poeppigiiLindl.,P. revoluta(Ruiz&Pav.) Garay,Restrepiella ophiocephala(Lindl.) Garay&Dunsterv.,Restrepia musciferaRchb. f. ex Lindl.,Scaphosepalum rapaxLuer,Stelis endresiiRchb. f.), four nonpleurothallid orchids (Cyrtopodium punctatum(L.) Lindl.,Encyclia cochleata(L.) Lemee,E. tampensis(Lindl.) Small,Paphiope‐dilumhybrid) and five tillandsioid bromeliads (Catopsis nutans(Sw.) Griseb.,Tillandsia fas‐ciculataSw.,T. streptophyllaScheidw.,T. strictaSoland.,T. tectorumE. Morr.) were assayed for permeability to Ca, S and P ions. Compared to leaves of the atmospheric bromeliads, those of the orchids proved less permeable to Ca and S. Moisture exchange profiles were determined for two of the bromeliads and three orchids; bromeliad leaves were able to rehydrate completely, orchid leaves only partially. Absorptive capacities of trichomes borne by five taxa were tested by autoradiographic analysis. Unlike bromeliad trichomes, those of the orchids exhibited no capacity to accumulate3H‐leucine. These results and other considerations described here suggest that, unlike tillandsioid bromeliads, neither the pleurothallid nor the nonpleurothallid orchids examined in this survey rely heavily on shoots for mineral and moisture procurement.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07856.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

The dorsiventral shoot system ofSelaginella martensiiis characterized by opposite pairs of ventral and dorsal leaves that are dimorphic in size and form. This study was undertaken to determine if the smaller dorsal leaf can be appropriately regarded as an arrested form of the larger leaf. Although the pattern of cell divisions and cell enlargement associated with leaf initiation is similar for both leaf types, the extent of localized growth results in distinctly larger primordia on the ventral side of the shoot. Ventral leaf primordia are also distinguished by the early formation of more extensive mesophyll tissue. Regression analysis of quantitative data on leaf length vs. position and leaf width vs. length indicates that the growth pattern of ventral and dorsal leaves is significantly different. These observations indicate that the developmental pathways of the dimorphic leaves ofSelaginella martensiido not diverge at a relatively late developmental stage, but rather can be distinguished from inception.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07857.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

The anisophyllous shoots ofSelaginella martensiiare characterized by opposite pairs of dorsal and ventral leaves which differ in size and form. This paper documents the processes of histogenesis for each leaf type and shows that both leaf types show a strong basipetal gradient of tissue maturation as indicated by cell size, distribution of cell division, cell vacuolation, intercellular space formation and stomatal differentiation. These processes are complete at an earlier stage of development in dorsal leaves (P7–8) than for ventral leaves (P12, 13). Measurement of cell number in the uppermost dermal layer indicate that cell divisions occur at a greater rate during ventral leaf development and observations of mitotic figures indicate that cell division occurs over a slightly longer time period in ventral leaves (through P6) as compared with dorsal leaves (through P5). While the morphological and histological differences that occur between the mature ventral and dorsal leaves begin to appear at or shortly after leaf inception, the general pattern of histogenesis of both types of leaf is similar. Histologically the dorsal leaf is primarily distinguished by a precocious maturation of tissues.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07858.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

The Gleicheniaceae, containing approximately 120 species, is a family of primitive ferns distributed throughout most of the tropics and subtropics. Historically the family was considered to be monogeneric; however, most recent authors using morphological, anatomical and cytological information have subdivided the group into 5 or 6 distinct genera. Some authors have even elevated certain species to family or ordinal levels (e.g.,PlatyzomaandStromatopteris). The distribution of flavonol‐3‐0‐glycosides supports the segregation of the Gleicheniaceae, sensu lato, into at least three groupings. Flavonoids similar to those identified within the Psilotaceae (flavones, biflavones, and C‐glycosylflavones) were not detected during this study.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07859.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Seasonal differences in recoverable underground reserves in stands ofSpartina alternifloraLoisel. were measured in Georgia and Delaware. They indicate that by winter substantial reserves are stored in both northern and southern marshes. Cycles of the quantity of stored reserves have greater amplitudes than cycles of the concentration of storage compounds reported in the literature. Maximum concentrations apparently occur at the same time as maximum storage tissue volumes. Seasonal measurements and defoliation studies in Delaware indicate that reserves are nearly exhausted by spring growth and that at least ⅓ are not replenished until after seed filling in the fall. This pattern of nearly complete utilization of reserves in spring with late fall replenishment may have an advantage for herbaceous perennial plants which are part of detritus based food webs. A cycle where substantial reserves are retained for canopy regeneration after early summer defoliation would be advantageous where a grazing web was dominant.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07860.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Both seasonal and lifetime allocation patterns were determined forS. pauciflosculosa, a woody composite, by monitoring biomass loss and gain of each age class in a population for one year. Seasonal allocation patterns were typical of woody plants in stressed environments and did not differ significantly among different aged plants of the same reproductive status. The standing biomass of a mature individual was partitioned as follows: roots 15%, stems 55%, leaves 19%, and reproductive tissues 11%. Lifetime allocation to these particular tissues were 5%, 15%, 50%, and 30% respectively. Lifetime allocation to reproduction was similar to values for related annuals. The implications of these findings for energy allocation theory are discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07861.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Electron microscopic observations of epidermal and cortical cells of the root tips of barley (Hordeum vulgareL.) grown in 192 mm NaCl and aged in 192 mm NaCl + 0.2 mm CaSO4revealed marked condensation of chromatin in the nuclei which was not observed in freshly cut tissue grown in the presence of 192 mM NaCl. Other changes due to salinity were observed, such as the increase of the number of ribosomes and of mitochondria and the appearance of translucent areas in slightly swollen mitochondria. The mechanism by which the nuclear changes occurred or their meaning for cell function are not understood.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07862.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Three phases of adhesion between the stock and scion are observable during the formation of a compatible autograft inSedum telephoidesand an incompatible heterograft betweenSedum telephoidesandSolanum pennellii. The first phase of adhesion is similar in both systems in that it 1) lasts 2 to 3 days, and 2) is characterized by an average increase in tensile strength of 1 g breaking weight (BW)/mm2graft area (GA)/day. In the compatibleSedumautograft, the second phase of adhesion lasts from Days 3 to 11 after grafting and is correlated with a 28‐fold increase in the tensile strength of the graft union to approximately 56 g BW/mm2GA by 11 days after grafting. The third phase of adhesion in the compatible autograft is characterized by a leveling off of the tensile strength of the graft union at approximately 56 g BW/mm2GA, roughly equal to that of an ungrafted internode. Graft formation is now complete. These results suggest that the ratio of the tensile strength of the graft union : tensile strength of a comparable ungrafted internode provides an estimate of the percent development of compatible autografts. In the incompatible heterograft betweenSedumandSolanum, Phase II adhesion 1) lasts from Days 2 to 5 after grafting, and 2) peaks at 12 g BW/mm2GA at 5 days after grafting. Phase III adhesion in the incompatible heterograft occurs subsequent to Day 5 after grafting and is characterized by an average decrease in the tensile strength of the graft union of 0.3 g BW/mm2GA/day. The results of this study are discussed relative to the quantitative contributions of various structural events to the tensile strength of a graft union.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07863.x

出版商:Wiley    

年代:1983

数据来源: WILEY