Blue light suppression alters cytokinin homeostasis in wheat leaves senescing under shading stress.

Blue light (BL) suppression accelerates the senescence rate of wheat (Triticum aestivum L.) leaves exposed to shading. In order to study whether this effect involves the alteration of different cytokinin (CK) metabolites, CK-degradation, as well as the expression profile of genes responsible of CK-perception, -inactivation, -reactivation and/or -turnover, leaf segments of 30 day-old plants were placed in boxes containing bi-distilled water and covered with blue (B) or green (G) light filters, which supplied a similar irradiance but differed in the percentage of BL transmitted (G << B). A neutral (N) filter was used as control. When appropriate, different CK metabolites or an inhibitor of CK-degradation were added in order to alter the endogenous CK levels. A rapid decrement of trans-zeatin (tZ) and cis-zeatin (cZ) content was observed after leaf excision, which progressed at a higher rate in treatment G than in the control and B treatments. Senescence progression correlated with an accumulation of glycosylated forms (particularly cZ-derivatives), and an increment of CK-degradation, both of which were slowed in the presence of BL. On the contrary, CK-reactivation (analyzed through TaGLU1-3 expression) was delayed in the absence of BL. When different CK were exogenously supplied, tZ was the only natural free base capable to emulate the senescence-retarding effect of BL. Even though the signaling components involved in the regulation of senescence rate and CK-homeostasis by BL remain elusive, our data suggest that changes in the expression profile and/or functioning of the transcription factor HY5 might play an important role.

The control of root growth by reactive oxygen species in Salix nigra Marsh. seedlings.

The production of reactive oxygen species (ROS) in specific regions of Salix seedlings roots seems essential for the normal growth of this organ. We examined the role of different ROS in the control of root development in Salix nigra seedlings, and explored possible mechanisms involved in the regulation of ROS generation and action. Root growth was not significantly affected by OH quenchers, while it was either partially or completely inhibited in the presence of H2O2 or O2·â» scavengers, respectively. O2·â» production was elevated in the root apex, particularly in the subapical meristem and protodermal zones. Apical O2·â» generation activity was correlated to a high level of either Cu/Zn superoxide dismutase protein as well as carbonylated proteins. While NADPH-oxidase (NOX) was probably the main source of O2·â» generation, the existence of other sources should not be discarded. O2·â» production was also high in root hairs during budding, but it markedly decreased when the hair began to actively elongate. Root hair formation increased in the presence of H2O2 scavengers, and was suppressed when H2O2 or peroxidase inhibitors were supplied. The negative effect of H2O2 was partially counteracted by a MAPKK inhibitor. Possible mechanisms of action of the different ROS in comparison with other plant model systems are discussed.

Gas exchange and carbon metabolism in two Prosopis species (Fabaceae) from semiarid habitats: effects of elevated CO2, N supply, and N source.

Predicting future plant and ecosystem responses to elevated CO(2) also requires an understanding of the role of other factors, especially soil nitrogen. This is particularly challenging for global aridlands where total N and the relative amounts of nitrate and ammonia vary both spatially and seasonally. We measured gas exchange and primary and secondary C metabolites in seedlings of two dominant aridland shrub species (Prosopis flexuosa [S America] and P. glandulosa [N America]) grown at ambient (350 ppm) or elevated (650 ppm) CO(2) and nitrogen at two levels (low [0.8 mM] and high [8.0 mM]) and at either 1 : 1 or 3 : 1 nitrate to ammonia. Whereas elevated CO(2) increased assimilation rate, water use efficiency, and primary carbon metabolites in both species, these increases were strongly contingent upon nitrogen availability. Elevated CO(2) did not increase secondary metabolites (i.e., phenolics). For these important aridland species, the effects of elevated CO(2) are strongly influenced by nitrogen availability and to a lesser extent by the relative amounts of nitrate and ammonia supplied, which underscores the importance of both the amount and chemical composition of soil nitrogen in mediating the potential responses of seedling growth and establishment of aridland plants under future CO(2)-enriched atmospheres.