Polarized microtubule deposition coincides with wall ingrowth formation in transfer cells ofVicia faba L. cotyledons

Summary The epidermal transfer cells in developingVicia faba L. cotyledons are highly polarized. Extensive wall ingrowths occur on their outer periclinal walls and extend part way down both anticlinal walls. This ingrowth development serves to increase the surface area of the plasma membrane and thus maximize porter-dependent uptake of sugars from the seed apoplasm. In contrast, the inner periclinal walls of these transfer cells do not form wall ingrowths. We have commenced a study of the mechanisms responsible for establishing this polarity by first analysing the microtubule (MT) cytoskeleton in developing transfer cells. Thin sections of fixed cotyledons embedded in methacrylate resin were processed for immunofluorescence microscopy using monoclonal anti--tubulin and counterstained with Calcofluor White to visualize wall ingrowths. In epidermal cells of young cotyledons where wall ingrowths were yet to develop, MT labelling was detected around all cortical regions of the cell. However, in cells where wall ingrowths were clearly established, MT labelling was detected almost exclusively in cortical regions adjacent to the wall ingrowths. Little, if any, MT labelling was detected on the anticlinal or inner periclinal walls of these cells. This distribution of MTs was most prominent in cells with well developed wall ingrowths. In these cells, a subpopulation of MTs were also detected emanating from the subcortex and extending towards the wall ingrowth region. The possible role of MT distribution in establishing transfer cell polarity and wall ingrowth formation is discussed.Abbreviations MT microtubule     

新疆盐生植物耐盐基因NHX转化甘蓝型油菜及其耐盐性的初步研究

以甘蓝型油菜带柄子叶为转化受体,通过根癌农杆菌EHA105(Agrobacterium tumefaciens)介导将盐角草(Salicornia)的Na /H 反向运输体基因NHX导入新疆主栽油菜1khp11品系,获得了抗卡那霉素的再生植株,并对影响遗传转化的一些关键因素进行了研究。实验结果表明:带柄子叶在含有2,4-D的培养基上经过2d短时间的预培养后在菌液浓度OD600为0.3时在28℃摇床浸染15min时卡那抗性绿苗率可达10%￣12%;经过抗性植株的PCR及RT-PCR检测证明外源基因已整合到油菜基因组中,并通过表型实验证实由于外源基因的导入提高了植株的耐盐能力。     

Metabolic significance of indoleacetylaspartic acid in developing cotton leaves

The formation of indoleacetylaspartic acid (IAAsp) and its metabolic significance were studied in the developing cotyledons and primary two leaves of cotton ( Gossypium barbadense L. cv. Giza 68, long staple). Levels of indoleacetic acid (IAA), IAAsp, bound IAA and degradation of tryptophan (Trp)-carboxyl-[¹⁴C] by enzyme extracts were estimated from leaf emergence to full expansion. The patterns were also followed in the two cotyledons before and after germination. The results suggest synthesis of IAAsp in response to either active Trp-conversion or hydrolysis of bound IAA. Ester IAA accumulating during leaf expansion, or other bound forms of IAA initially stored in the cotyledons may be the substances hydrolysed. IAAsp appears to be accumulated during phases of low demand and to be exhausted during phases of high demand on IAA. Synthesis and hydrolysis of the conjugate may, therefore, influence the steady state concentration of the hormone during leaf development.     

Constraints on tree seedling establishment after fires: passing the germination bottlenecks

• Persistence and colonization by tree species in an environment following a fire depends on the effects on seed germination and seedling development. We used seeds of Kielmeyera coriacea and Qualea parviflora as a model to test the effects of high temperatures on germination and initial development of tree seedlings.
• We exposed the seeds to heat flow (70, 100, 130, 150 or 170 °C) for 2 or 5 min and compared the germination with that of unheated seeds (control). Seedlings were then harvested after 3, 7 or 15 days to evaluate aerial and root mass, root:shoot ratio, presence of cotyledon opening, true leaves, and secondary roots.
• We found no effect on germination for seeds exposed to temperatures ≥150 °C. However, germination was significantly reduced for seeds exposed to 100 °C for both 2 and 5 min. The mass of 15-day-old K. coriacea seedlings was smaller when seeds were heated at 70 °C for 5 min or at temperatures higher or equal to 100 °C. Qualea parviflora seedlings did not show any difference in mass, but there were marginal differences in the presence of roots and the opening of cotyledons. Kielmeyera coriacea seedlings allocated biomass faster than Q. parviflora.
• High temperatures affect both quantity and quality of germinable seeds, as well as biomass allocation during initial seedling development. These factors may explain the decrease in seedlings observed after fire, suggesting a bottleneck effect that influences population dynamics and species persistence in systems with frequent fires.