春小麦胚芽伸长过程中渗透调节与能量代谢

本文用PEG模拟水分亏缺对春小麦红芒麦和绵阳11号胚芽伸长过程中生长、膨压、渗透势、水势和渗透调节能力与ATP含量、能荷变化及能量代谢间的关系进行了研究。结果表明,通过降低能荷,改变分解代谢与合成代谢的比率,使渗透调节物质积累,增加了幼苗的吸水能力,从而使其在一定的ATP能量水平上维持缓慢生长;抗旱品种红芒麦在水分亏缺下成苗速率较快,能保持一定的ATP能量水平和能荷值,渗透调节和吸水能力都比较强。     

甘蔗节间伸长过程赤霉素生物合成关键基因的表达及相关植物激素动态变化

以甘蔗(Saccharum officinarum)优良品种桂糖42号(GT42)为研究材料, 分别于未伸长期(9-10叶龄以前) (Ls1)、伸长初期(12-13叶龄) (Ls2)和伸长盛期(15-16叶龄) (Ls3)取甘蔗第2片真叶(自顶部起)对应的节间组织, 测定其赤霉素(GA)、生长素(IAA)、油菜素甾醇(BR)、细胞分裂素(CTK)、乙烯(ETH)和脱落酸(ABA)的含量, 并通过实时荧光定量PCR (qRT-PCR)分析赤霉素合成途径关键基因GA₂₀氧化酶基因(GA20-Oxidase1)、赤霉素受体基因(GID1)和DELLA蛋白编码基因(GAI)的差异表达。结果表明, 在甘蔗伸长期间, GA和IAA含量呈现上升趋势, CTK和ABA含量呈下降趋势, ETH含量先上升后下降, BR含量则变化不明显; GA20-Oxidase1和GID1的表达呈上升趋势, 而GAI的表达则呈下降趋势, 这与相关植物激素的变化基本一致。综上, 甘蔗节间伸长过程主要与GA和IAA相关, 其次为CTK和ABA, 而ETH受到IAA的调控影响节间伸长; 植物激素间通过相互作用调控GA20-Oxidase1、GID1和GAI的表达, 影响GA含量和GA的信号转导过程, 进而影响甘蔗节间的伸长。该研究揭示了甘蔗节间伸长过程中赤霉素生物合成途径和信号转导关键基因的差异表达及植物激素含量的动态变化规律。     

Changes in cell-wall polysaccharide composition of developingNitella internodes

Changes in the uronide, neutral-polysacharide, and cellulose composition of the cell wall ofNitella axillaris Braun were followed throughout development of the internodes and correlated with changes in growth rate. As the cells increased in length from 4 to 80 mm during development, the relative growth rate decreased. Cell wall thickness, as measured by wall density, increased in direct proportion to diameter, indicating that cell-wall stress did not change during elogation. Cell-wall analyses were adapted to allow determination of the composition of the wall of single cells. The total amounts of uronides, neutral sugars and cellulose all increased during development. However, as the growth rate decreased, the relative proportions of uronides and neutral sugars, expressed as percent of the dry weight of the wall, decreased, while the proportion of cellulose increased. The neutral sugars liberated upon hydrolysis ofNitella walls are qualitatively similar to those found in hydrolysates of higher plant cell walls: glucose, xylose, mannose, galactose, arabinose fucose and rhamnose. Only the percentage of galactose was found to increase in walls of mature cells, while the percentage of all other sugars decreased. The rate of apposition (g of wall material deposited per unit wall surface area per hour) of neutral polysaccharides decreased rapidly with decreasing growth rate during the early stages of development. The rate of apposition of uronides decreased more steadily throughout development, while that of cellulose, after an early decline, remained constant until dropping off at the end of the elongation period. These correlations between decreasing growth rate and decreasing rate of apposition of neutral sugars and uronides indicate that synthesis of these cell-wall components could be involved in the regulation of the rate of cell elongation inNitella.     

Shoot growth phenology of co-existing evergreen and deciduous species in an oak forest

Shoot growth phenology was compared for the saplings of evergreen and deciduous woody species sharing the same microsite. Growth initiation occurred earlier in evergreens (among co-stratal species) while deciduous species completed their growth earlier. Shoot growth rate was significantly greater (P<0.01) for deciduous trees than evergreen trees. The amount of shoot elongations and shoot diameter was also significantly greater (P<0.01) for deciduous trees than evergreens. On the other hand, among shrubs the amount of shoot elongation and shoot diameter was greater for evergreens but the rate of elongation and diameter was more or less similar for both. The duration of shoot elongation and shoot diameter was significantly longer in evergreens than the deciduous species. Leaf packing (number of leaves per shoot) was significantly more dense in evergreen trees (P<0.01) than in deciduous tree species. Leaf packing was more dense in evergreen than deciduous shrubs but the difference was not significant. Leaf area (per individual leaf) at full expansion was significantly greater (P<0.01) in deciduous species. Leaf dry mass and specific leaf mass in the initial stage was significantly greater for evergreen species than for deciduous species. The number of buds/10 cm of shoot was higher in evergreens. However, the per cent mortality was also higher in them.     

Alternatives to telomerase: keeping linear chromosomes via telomeric circles

Recombination is often capable of lengthening telomeres in situations where telomerase is absent. This recombinational telomere maintenance is often accompanied by telomeric instability including the accumulation of extrachromosomal telomeric circles (t-circles). Recent results of in vivo and in vitro experiments have suggested that t-circles can lead to the production of extended stretches of telomeric DNA by serving as templates for rolling-circle synthesis. This implies that t-circles can provide an efficient means of telomere elongation. The existence of t-circles in both nuclear and mitochondrial compartments of distantly related species suggests that they may be important contributors to an evolutionary conserved telomerase-independent mechanism of maintenance of telomeric tandem arrays.