Effects of pollination intensity on Lesquerella fendleri seed set: variation among plants

 The amount of pollen arriving on a flower can be an important determinant of seed production. I investigated the effect of varying pollen loads on seed set of the perennial desert mustard Lesquerella fendleri. To do this, I quantified the dose response relationship between stigmatic pollen load and seed set per fruit using over 400 flowers from 13 greenhouse-grown plants. Seed set per fruit generally increased with pollen up to about 100 pollen grains, then reached a plateau. A negative exponential regression of seed set on pollen load for the pooled data explained less than 10% of the observed variation in seeds per fruit. However, accounting for variation among individual plants in the dose-response relationship increased explained variation to 40%, indicating that plants responded differently to the same amount of available pollen. Plants varied little in the initial slope of the dose-response curve, but differed substantially in the asymptote, which ranged from 3 to 16 seeds. This limit is not imposed by ovule number, and may instead result from variation among plants in vigor, propensity to abort seeds, or in gender specialization. Such variation among plants in dose-response relationships has important consequences for understanding pollination limitation and pollen competition. Received: 29 January 1996 / Accepted: 6 August 1996     

Growth inhibition and recovery in freeze-substitutedLilium longiflorum pollen tubes: structural effects of caffeine

Summary In an attempt to correlate structural effects with the known dissipation of the tip-focused Ca²⁺ gradient caused by caffeine, we have examined the ultrastructure of caffeine-treated lily pollen tubes prepared by rapid freeze fixation and freeze substitution. We show that treatment with caffeine results in a rapid rearrangement of secretory vesicles at the pollen tube tip; the normal cone-shaped array of vesicles is rapidly dispersed. In addition, microfilament bundles appear in the tip region, where they had previously been excluded. Delocalized vesicle fusion continues in the presence of caffeine but tube extension ceases. Removal of caffeine from the growth medium initially causes tip swelling, delocalized vesicle fusion and presence of microfilaments well into the tip before normal structure and growth resume, concurrent with the previously reported return to a normal Ca²⁺ gradient.Abbreviations ER endoplasmic reticulum - MES 2-[N-morpholino] ethanesulfonic acid - MFs microfilaments     

Loss of callose in the stigma papillae does not affect the Brassica self-incompatibility phenotype

As part of the Brassicaceae self-incompatibility response, callose is deposited in the stigma papillar cells. To determine if callose plays an important role in the rejection of incompatible pollen by the stigma, transgenic Brassica napus. L. plants were produced which express the tobacco β-1,3-glucanase cDNA (the enzyme which degrades callose) in the stigma papillae. Using aniline blue fluorescence, little or no callose was detected in the papillar cells of transgenic stigmas. However, the self-incompatibility system appeared to be unaffected based on the lack of pollen tube growth and the subsequent lack of seed set. The transgene had no effect on compatible pollinations. Thus, while callose deposition is associated with the B. napus self-incompatibility response, it is not required for the rejection of incompatible pollen. Received: 14 March 1997 / Accepted: 15 April 1997     

Main role of self-pollination rate on reproductive allocations in pseudogamous apomicts

 Most apomicts are hermaphroditic and pseudogamous (pollination is necessary to trigger parthenogenesis). In these plants, fitness depends on the number of progeny obtained by maternal reproduction. We determined the evolutionary stable strategy for male and female sex allocation. We show that the efficiency of pollination determines male and female resource allocations. Predictions are made of these allocations, of pollen/ovule ratio and of seed-set. We show that self-compatibility in apomicts is necessary for the maintenance of an apomictic population, and thus can account for the association between the loss of self-incompatibility and pseudogamous apomixis. In contrast to sexuals, male investment in pseudogamous apomicts increases with the rate of self-pollination. Received: 15 June 1996 / Accepted: 20 September 1996     

A comparative ultrastructural analysis of exine pattern development in wild-typeArabidopsis and a mutant defective in pattern formation

Summary In order to identify factors necessary for the establishment of the reticulate pollen wall pattern, we have characterized a T-DNA tagged mutant ofArabidopsis thaliana that is defective in pattern formation. This study reports the results of an ultrastructural comparison of pollen wall formation in the mutant to wall development in wild-type plants. Pollen wall development in the mutant parallels that of wild-type until the early tetrad stage. At this point in wild-type plants, the microspore plasma membrane assumes a regular pattern of ridges and valleys. Initial sporopollenin deposition occurs on the ridges marking the beginning of probacula formation. In contrast, the plasma membrane in the mutant appears irregular with flattened protuberances and rare invaginations. As a result, the wild-type regular pattern of ridges and valleys is not formed. Sporopollenin is randomly deposited on the plasma membrane and aggregates on the locule wall; it is not anchored to the membrane. Our finding that the mutation blocks the normal invagination of the plasma membrane and disrupts the proper deposition of sporopollenin during wall formation suggests that the mutation could be in a gene responsible for pattern formation. These results also provide direct evidence that the plasma membrane plays a critical role in the establishment of the pollen wall pattern.     

Changes in soluble sugars in relation to desiccation tolerance and effects of dehydration on freezing characteristics of Acer platanoides and Acer pseudoplatanus seeds

The role of soluble sugars in desiccation tolerance was investigated in seeds of two species from the genus Acer: Norway maple (Acer platanoides L.) — tolerant and sycamore (Acer pseudoplatanus L.) — intolerant to dehydration. During two years of observations it was found that seeds of Norway maple acquire desiccation tolerance at the end of August i.e. about 125 days after flowering (DAF). During seed development, the transition from intolerant to tolerant state in Norway maple seeds was accompanied by the accumulation in seed tissues of raffinose, stachyose and sucrose. The sucrose/raffinose ratio in Norway maple seeds was lower than in sycamore. In mature Norway maple seeds sucrose and raffinose contents were higher than in sycamore. It was concluded, that soluble sugars such as sucrose, raffinose and stachyose may play an important role in desiccation tolerance and/or intolerance of Norway maple and sycamore seeds. Differential thermal analysis (DTA) was used to study the relationship between desiccation sensitivity and the state of water in seed tissues. The level of non-freezable water was the same in both analysed seed species, but the temperature of water crystallization during desiccation was lower in sycamore seeds.     

Functional maturation of mouse CD4+CD8- thymocytes induced by medullary-type thymus epithelial cells

Murine CD4⁺CD8^- (CD4SP) thymocyte subset is a heterogeneous population, in which the Qa-2^- cells are less functional, whereas the Qa-2⁺ cells are fully functional. Evidence is provided here that the transition from Qa-2^- to Qa-2⁺ CD4SP thymocytes is an intrathymic process of differentiation induced by thymic medullary-type epithelial cells. The separated Qa-2^-CD4SP could be induced to express Qa-2 molecules up to 84%- 89% of the total viable celb after cocultured for 3d with MTEC1 cells, a murine thymic medullary type epithelial cell line established in our laboratory. Kinetic study showed that both the percentage of Qa-2⁺ cells and the density of the expressed Qa-2 molecules on CD4SP thymocytes induced by MTEC1 were progressively increasing in 72-h cultures. The MTECl-induced Qa-2⁺CD4SP thymocytes were fully functional, which exhibited capabilities of proliferation and cytokine secretion in response to Con A stimulation as high as those of freshly isolated Qa-2⁺CD4SP thymocytes. The profile of cytokines secreted by MTECl-induced Qa-2⁺CD4SP thymocytes was Thy 0 type specified by the production of IL-2, IL-4 and IL-6. The results suggest that Qa-2^-CD4SP thymocytes may give rise to the Qa-2⁺CD4SP thymocytes, and acquire fully functional competence in thymic medulla under the foster of local epithelial cells.     

Variability in maturation and germination from white spruce somatic embryos,as affected by age and use of solid or liquid culture

Summary The yield of morphologically normal Stage 3 somatic embryos of white spruce [Picea glauca (Moench) Voss], and subsequent germinability, was affected by culture age and use of solid and/or liquid culture growth conditions. Of the conditions that were compared, best results were obtained with cultures up to 3 yr old that had been continuously grown in liquid medium. Such material yielded up to 374 morphologically normal Stage 3 embryos per g f. wt. inoculum, when routinely pretreated using a 1 wk 2,4-dichlorophenoxyacetic acid-free period before maturation. By comparison the continual use of solid culture conditions resulted in lower yields (5/g f. wt. inoculum), and the use of solid medium in combination with liquid medium showed a greater affect of age on the production of normal Stage 3 embryos (348/g f. wt at 1.5 yr down to 19/g f. wt. at 3 yr) over the age range tested. In the absence of culture pretreatment, the oldest liquid cultures yielded only 44 normal Stage 3 embryos/g f. wt. inoculum, and the comparable solid to liquid cultures yielded 1.3/g f. wt. inoculum. The number of aberrant Stage 3 embryos in older cultures was reduced as a result of culture pretreatment; for example, in the oldest liquid cultures these represented 83% of the Stage 3 embryo population without pretreatment and 45% with pretreatment. Normal Stage 3 somatic embryo yield and germination characteristics (radicle and epicotyl development) were informative in distinguishing among the conditions studied. Germination characteristics were especially important when maturation responses were incapable of distinguishing among age classes. NRCC Contribution no. 38462.     

国产葛属植物花粉形态的研究

对国产葛属ＰｕｅｒａｒａｉＤＣ．７种１变种植物花粉的光学显微镜、扫描电镜以及２种１变种的透射电镜观察表明：花粉形态各具特征;表面纹饰类型包括穿孔状（一般直径小于网脊直径或稍等,孔穴中无或少颗粒）、细网纹（网眼直径约与网脊直径相等或略细,网眼内具颗粒）、粗网纹（网眼直径大于网脊直径、网眼内具成片的众多颗粒）;孔沟类型为具孔膜或孔盖,孔膜常成孔桥．上述结果,表明葛属植物７种１变种的花粉形态是有区别的,从覆盖层等形态结构可以推测其亲缘关系,亦可看到部分的演化．     

中国蒿属植物比较形态和解剖学研究 Ⅱ花粉形态

本文通过光学显微镜和扫描电镜,观察国产菊科蒿属２亚属７组５８种代表物的花粉形态,结合有关资料以及菊科１２族,３０属代表植物花粉作比较,分析研究,取得以下结果：１．蒿属的花粉特征具有高度的一致性。主要体现在：花粉呈球形或近球形,极面观的三形圆形,赤道面观为圆形或椭圆形。