Antagonism between abscisic acid and gibberellins is partially mediated by ascorbic acid during seed germination in rice

The antagonism between abscisic acid (ABA) and gibberellin (GA) plays a key role in controlling seed germination,^1,2 but the mechanism of antagonism during this process is not known. In the associated study,³ we investigated the relationship among ABA, reactive oxygen species (ROS), ascorbic acid (ASC) and GA during rice seed germination. ROS production is reduced by ABA, which hence results in decreasing ASC accumulation during imbibition. GA accumulation was also suppressed by a reduced ROS and ASC level, whereas application of exogenous ASC can partially rescue seed germination from ABA treatment. Further results show that production of ASC, which acts as a substrate in GA biosynthesis, was significantly inhibited by lycorine which thus suppressed the accumulation of GA. Consequently, expression of GA biosynthesis genes was suppressed by the low levels of ROS and ASC in ABA-treated seeds. These studies reveal a new role for ASC in mediating the antagonism between ABA and GA during seed germination in rice.     

在控制条件下光敏核雄性不育粳稻抽穗与结实的光周期与温度反应特性

在人工气候室研究了１５个光敏核雄性不育系粳稻抽穗与结实对日长与温度的反应特性。１个品系抽穗的光周期反应极弱,８个中等;６个强;农垦５８Ｓ与其原种反应均强．但ＰＳＰ略有差异;而且农垦５８Ｓ在雌雄蕊原基分化前移入ＬＤ,不但抽穗延迟且结实率显著降低,而农垦５８抽穗虽延迟但结实正常。高温抽穗促进车品系间差异大,从０～４ｄ．９％,较多为２２％～３８％。１５个不育结实的光周期反应明显;它们在高温、低温、ＬＤ下结实明显受阻,有的即使在ＳＤ下结实率亦很低。说明它们雄性细胞较孱弱易受不良光、温条件危害,可能是遗传上有缺陷;繁种时应注意地区的光、温条件,并利用ＳＤ下结实尚可的品系。     

Dwarf and deformed flower 1, encoding an F‐box protein,is critical for vegetative and floral development in rice (Oryza sativa L.)

Recent studies have shown that F‐box proteins constitute a large family in eukaryotes, and play pivotal roles in regulating various developmental processes in plants. However, their functions in monocots are still obscure. In this study, we characterized a recessive mutant dwarf and deformed flower 1‐1 (ddf1‐1) in Oryza sativa (rice). The mutant is abnormal in both vegetative and reproductive development, with significant size reduction in all organs except the spikelet. DDF1 controls organ size by regulating both cell division and cell expansion. In the ddf1‐1 spikelet, the specification of floral organs in whorls 2 and 3 is altered, with most lodicules and stamens being transformed into glume‐like organs and pistil‐like organs, respectively, but the specification of lemma/palea and pistil in whorls 1 and 4 is not affected. DDF1 encodes an F‐box protein anchored in the nucleolus, and is expressed in almost all vegetative and reproductive tissues. Consistent with the mutant floral phenotype, DDF1 positively regulates B‐class genes OsMADS4 and OsMADS16, and negatively regulates pistil specification gene DL. In addition, DDF1 also negatively regulates the Arabidopsis LFY ortholog APO2, implying a functional connection between DDF1 and APO2. Collectively, these results revealed that DDF1, as a newly identified F‐box gene, is a crucial genetic factor with pleiotropic functions for both vegetative growth and floral organ specification in rice. These findings provide additional insights into the molecular mechanism controlling monocot vegetative and reproductive development.     

Root hair-specific expansins modulate root hair elongation in rice

Root hair growth requires intensive cell‐wall modification. This study demonstrates that root hair‐specific expansin As, a sub‐clade of the cell wall‐loosening expansin proteins, are required for root hair elongation in rice (Oryza sativa L.). We identified a gene encoding EXPA17 (OsEXPA17) from a rice mutant with short root hairs. Promoter::reporter transgenic lines exhibited exclusive OsEXPA17 expression in root hair cells. The OsEXPA17 mutant protein (OsexpA17) contained a point mutation, causing a change in the amino acid sequence (Gly104→Arg). This amino acid alteration is predicted to disrupt a highly conserved disulfide bond in the mutant. Suppression of OsEXPA17 by RNA interference further confirmed requirement for the gene in root hair elongation. Complementation of the OsEXPA17 mutant with other root hair EXPAs (OsEXPA30 and Arabidopsis EXPA7) can restore root hair elongation, indicating functional conservation of these root hair EXPAs in monocots and dicots. These results demonstrate that members of the root hair EXPA sub‐clade play a crucial role in root hair cell elongation in Graminaceae.     

Sequential and non-sequential pattern of monocarpic senescence in two rice cultivars

Two rice ( Oryza sativa L.) cultivars viz. Ratna (dwarf, photoperiod insensitive) and Masuri (tall, photoperiod sensitive) were selected to analyse their mode of senescence. At the vegetative stage, leaf senescence, expressed as the loss of chlorophyll and protein and a decline in the activities of catalase and alkaline pyrophosphatase, was found to be a function of chronological age (sequential) in both cultivars. With advancing reproductive development, cultivar Masuri retained this sequential mode but cultivar Ratna showed a non-sequential mode of senescence where the flag leaf senesced earlier than the older second leaf, unlike that observed at the vegetative stage. Masuri showed a more rapid senescence than Ratna. In both cultivars, excision of any leaf during anthesis initially retarded the senescence of the remaining leaves on the defoliated plants but soon after, at the grain maturation stage, the leaf senescence started at a higher rate compared with that of the intact control plant. In Ratna, when either the second or the third leaf was removed, the flag leaf senesced faster than that of the unexcised control plant. In Masuri, when either the flag or the third leaf was removed, the second leaf senesced earlier than that of the intact control. In both cultivars, excision of the third leaf showed the least detrimental effect on yield. The greatest detrimental effect on grain yield per plant was observed in Ratna when the flag leaf was removed and in Masuri when the second leaf was removed. Mobilization of metabolites from the source leaf to the sink and the consequent depletion in the leaf as the cause of senescence is discussed.     

广东白腹巨鼠的G带核型和银染色

本文报道了广东白腹巨鼠的核型、G带和银染色。结果表明,二倍体染色体数目为2n=40,常染色体包括4对近端着丝粒染色体,6对末端着丝粒染色体,8对中着丝粒染色体,1对近中着丝粒染色体。性染色体XY为大小不等的末端着丝粒染色体。G分带可鉴别每对染色体的特征,Ag-NORs位于1对近端着丝粒染色体（3号）和2对中等大小的末端着丝粒染色体。