Degradation of ribulose-1,5-bisphosphate carboxylase and chlorophyll in senescing barley leaf segments triggered by jasmonic acid methylester, and counteraction by cytokinin

Barley ( Hordeum vulgare L. cv. Salome) primary leaf segments responded to the application of a putative plant growth regulator, ± jasmonic acid methylester (JA-Me). with accelerated senescence, as indicated by the loss of chlorophyll and the rapid decrease in activity and immunoreactive protein content of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBP carboxylase, EC 4.1.1.39). The senescence-promoting action of JA-Me differed in light and in darkness; e.g. the initial rates of chlorophyll and RuBP carboxylase breakdown were markedly higher in light than in darkness in the presence of 4.10⁻⁵ M JA-Me. Cytokinin (benzyladenine, 4.10⁻⁵ M ) stopped the loss of chlorophyll and RuBP carboxylase during senescence; however, the rapid drop induced by JA-Me in the early phase of leaf segment senescence could not be prevented by concomitant or previous addition of BA. On the other hand, BA added 24 h after JA-Me application resulted in a recovery of chlorophyll and RuBP carboxylase at the later stages, indicating a possible rapid inactivation of JA-Me in the tissues. The activities of a number of other chloroplastic and cytosolic enzymes were not significantly altered in JA-Me-treated leaf segments compared with controls floated on water. Time-dependent chlorophyll decrease in isolated chloroplasts did not change upon JA-Me addition to the isolated organelles. It is suggested that JA-Me acts on chloroplast senescence by promoting cytoplasic events which eventually bring about the degradation of chloroplast constituents.     

Regeneration of whole plants from hypocotyl-, root-, and leaf-derived tissue cultures of the pasture legume Stylosanthes guyanensis

Callus cultures were established on Murashige and Skoog medium from seedling hypocotyls and roots of Slylosanlhes guyanensis (Aubl.) Sw. cv. Cook and from leaves of 6-month-old) plants. Shoots developed in primary calli derived from seedling tissue with a number of benzyladenine or kinetin and naphthaleneacetic acid combinations. Shoot formation on primary leaf callus, occurred with 2.0 mg/1 benzyladenine and 2.0 or 1.0 mg/l naphthaieneacetic acid. Undifferentiated callus from all three sources was induced and maintained on medium with 2.0 mg/1 kinetin and 2.0 mg/1 2, 4-dichlorophenoxyacede acid in the dark. Shoot formation and regeneration of whole plants from these calli were achieved at high frequencies. The most successful combination of phytohormones for the induction of shoot development in undifferentiated callus, was 2.0 mg/1 benzyladenine and 1.0 mg/1 naphthaleneacetic acid. The regenerated plants showed no phenotypic abnormalities.     

几种木本植物插穗生根与内源IAA,ABA的关系

迄今为止,传统的插条繁殖仍是林业和园林工作者获得良种无性系和培育苗木的重要途径。在影响插穗不定根形成内外因素中,植物内源激素水平和生长调节剂应用占有重要地位。已知第一个根原基细胞的分裂依赖于内源生长素或外源的生长调节剂(Hartmann 1983,Haissig 1974),低浓度的ABA(1.26～20μg/ml)能促进     

Gibberellins, brassinosteroids and light-regulated development

The regulation of plant development by light requires the action of several well-studied plant hormones. However, the mechanism by which light and hormones affect identical developmental responses remains unclear. Recently, studies of mutants altered in light signal perception or transduction have suggested a role for gibberellins and brassinosteroids in light-regulated development. For instance, mutants in the major light-stable phytochrome from several plant species exhibit altered responsiveness to, or metabolism of, gibberellins. In contrast, mutants that develop as light-grown plants in the absence of light have implicated a role for brassinosteroids in the control of cell elongation, the expression of photoregulated genes, and the promotion of apical dominance, leaf senescence and male fertility. Future studies should help elucidate whether light and hormones independently affect these developmental responses or whether hormones are involved in the sequence of events initiated by excitation of photoreceptors.     

Phytohormone-like substances produced by single and mixed diazotrophic cultures of Azospirillum and Arthrobacter

The production of phytohormone-like substances byAzospirillum brasilense andArthrobacter giacomelloi were investigated in single and mixed batch cultures under diazotrophic conditions. The mixed culture showed higher productivity of gibberellins and cytokinins.     

Influence of plant maturity, shoot reproduction and sex on vegetative growth in the dioecious plant Urtica dioica

Background and Aims

Stinging nettle (Urtica dioica) is a herbaceous, dioecious perennial that is widely distributed around the world, reproduces both sexually and asexually, and is characterized by rapid growth. This work was aimed at evaluating the effects of plant maturity, shoot reproduction and sex on the growth of leaves and shoots.

Methods

Growth rates of apical shoots, together with foliar levels of phytohormones (cytokinins, auxins, absicisic acid, jasmonic acid and salicylic acid) and other indicators of leaf physiology (water contents, photosynthetic pigments, α-tocopherol and F_v/F_m ratios) were measured in juvenile and mature plants, with a distinction made between reproductive and non-reproductive shoots in both males and females. Vegetative growth rates were not only evaluated in field-grown plants, but also in cuttings obtained from these plants. All measurements were performed during an active vegetative growth phase in autumn, a few months after mature plants reproduced during spring and summer.

Key Results

Vegetative growth rates in mature plants were drastically reduced compared with juvenile ones (48 % and 78 % for number of leaves and leaf biomass produced per day, respectively), which was associated with a loss of photosynthetic pigments (up to 24 % and 48 % for chlorophylls and carotenoids, respectively) and increases of α-tocopherol (up to 2·7-fold), while endogenous levels of phytohormones did not differ between mature and juvenile plants. Reductions in vegetative growth were particularly evident in reproductive shoots of mature plants, and occurred similarly in both males and females.

Conclusions

It is concluded that (a) plant maturity reduces vegetative growth in U. dioica, (b) effects of plant maturity are evident both in reproductive and non-reproductive shoots, but particularly in the former, and (c) these changes occur similarly in both male and female plants.     

Sex-related adaptive responses of Populus cathayana to photoperiod transitions

Populus cathayana Rehd., a dioecious tree species, occupies a wide range of habitats in southwest China. Both males and females were grown under two regimes of photoperiod, from mid-length to short-day photoperiod (SD shift), or to long-day photoperiod (LD shift). SD shift triggered leaf senescence in both males and females by decreasing net photosynthesis rate ( A ), transpiration ( E ), and chlorophyll pigment ( Chl ), non-structural carbohydrate (NSC) and indoleacetic acid (IAA) contents, while increasing abscisic acid (ABA), malonaldehyde (MDA) and free proline (Pro) contents. The antioxidant enzyme (e.g. POD, CAT and SOD) activities and capability to maintain ultrastructural integrity also decreased under SD shift. Males exhibited faster leaf senescence than did females, as shown by greater decreases in A , E , Chl and IAA. However, males maintained a less senescent stage than did females, as indicated by higher values of A , Chl , NSC, IAA and antioxidant enzyme activities. Conversely, A , E , NSC and IAA contents and antioxidant enzyme activities were enhanced by lower O₂^•− in females, whereas reduced by higher O₂^•− in males under LD shift. Such sex-dependent responses of P. cathayana to photoperiod transitions showed that males and females possess different adaptabilities, which may relate to sex-specific leaf senescence speed under changing environments.     

柽柳根对管花肉苁蓉寄生的反应

采用石蜡切片技术以及酶联免疫法对管花肉苁蓉的寄主柽柳根进行研究,结果表明：接种有管花肉苁蓉的柽柳根随着管花肉苁蓉的生长而增粗,其初生导管有黄色粘性物质阻塞,这些阻塞物中含有糖类和脂类物质,随着管花肉苁蓉的生长而消失。这可能与柽柳根内源激素脱落酸（ABA）和茉莉酸（JA）的调控有关。     

灌浆期高温对水稻光合特性、内源激素和稻米品质的影响

以2个籼稻品种:温度钝感型品种K30和温度敏感型品种R21为材料,利用人工气候室控温,在水稻灌浆期设置高温(日均温度34.9℃)和适温(日均温度28.0℃)处理,测定不同灌浆时期(5,10,15,20,25d和30d)光合特性、内源激素含量及稻米品质的变化。结果表明,高温增强了K30的光合能力,K30高温处理净光合速率(Pn)在整个灌浆期都明显高于对照;R21在灌浆前期(5、10d和15d)高温处理与适温处理Pn差异不明显,在灌浆后期(20、25d和30d)高温处理Pn下降。高温增加了K30叶片和籽粒脱落酸(ABA)含量;而R21高温处理和适温处理叶片与籽粒ABA含量的对比不明显。高温处理对两个水稻品种叶片和籽粒赤霉素(GA3)与生长素(IAA)含量也有不同程度影响。高温胁迫降低稻米品质,但K30比R21表现出更强的温度钝感特性。