Lalonde S, Morse D, Saini H S
Institut de recherche en biologie végétale, Université de Montréal, Canada.
Plant Mol Biol. 1997 Jun;34(3):445-53. doi: 10.1023/a:1005882118506.
In wheat (Triticum aestivum L.), water deficit during meiosis in the microspore mother cells (MMCs) induces pollen abortion, resulting in the failure of fertilization and a reduction in grain set. In stressed plants, meiosis in MMCs proceeds normally but subsequent pollen development is arrested. Unlike normal pollen grains, which accumulate starch during the late maturation phase, stress-affected anthers contain pollen grains with little or no starch. Stress also alters the normal distribution of starch in the anther wall and connective tissue. To determine how starch biosynthesis is regulated within the developing anthers of stressed plants, we studied the expression of ADP-glucose pyrophosphorylase (AGP), which catalyzes the rate limiting step of starch biosynthesis. Two partial-length cDNAs corresponding to the large subunit of AGP were amplified by RT-PCR from anther RNA, and used as probes to monitor AGP expression in developing anthers of normal and water-stressed plants. These clones, WAL1 and WAL2, had identical deduced amino acid sequences and shared 96% sequence identity at the nucleic acid level. In normal anthers, AGP expression was biphasic, indicating that AGP expression is required for starch biosynthesis both during meiosis and later during pollen maturation. AGP expression in stressed anthers was not affected during the first phase of starch accumulation, but was strongly inhibited during the second phase. We conclude from these results that the reduced starch deposition later in the development of stressed pollen could be the result of a lower expression of AGP. However, this inhibition of AGP expression is unlikely to be the primary cause of male sterility because anatomical symptoms of pollen abortion are observed prior to the time when AGP expression is inhibited.
在小麦（普通小麦）中，小孢子母细胞减数分裂期间的水分亏缺会诱导花粉败育，导致受精失败和结实率降低。在受胁迫的植株中，小孢子母细胞的减数分裂正常进行，但随后的花粉发育会停滞。与正常花粉粒不同，正常花粉粒在成熟后期积累淀粉，而受胁迫影响的花药中的花粉粒几乎不含淀粉或完全没有淀粉。胁迫还会改变花药壁和连接组织中淀粉的正常分布。为了确定受胁迫植株发育中的花药内淀粉生物合成是如何被调控的，我们研究了ADP - 葡萄糖焦磷酸化酶（AGP）的表达，该酶催化淀粉生物合成的限速步骤。通过RT - PCR从花药RNA中扩增出两个对应于AGP大亚基的部分长度cDNA，并将其用作探针来监测正常和水分胁迫植株发育中的花药中AGP的表达。这些克隆，WAL1和WAL2，具有相同的推导氨基酸序列，在核酸水平上有96%的序列同一性。在正常花药中，AGP表达是双相的，这表明在减数分裂期间以及花粉成熟后期淀粉生物合成均需要AGP表达。在受胁迫的花药中，AGP表达在淀粉积累的第一阶段不受影响，但在第二阶段受到强烈抑制。从这些结果我们得出结论，受胁迫花粉发育后期淀粉沉积减少可能是AGP表达降低的结果。然而，AGP表达的这种抑制不太可能是雄性不育的主要原因，因为在AGP表达受到抑制之前就观察到了花粉败育的解剖学症状。
