Physiological responses of two rice (Oryza sativa L.) genotypes to chilling stress at seedling stage

In this study, quantitative changes of dry matter, proline and total soluble protein in shoot and root, stomatal conductance (gs), total chlorophyll, chlorophyll stability index (CSI) and soil and plant analyzer development (SPAD) number of latest fully-expanded leaves were determined in an Iranian coldsensitive rice genotype (Hoveizeh) in comparison to an international check genotype (IRCTN34, coldtolerant). The hydroponic experiment was arranged in a completely randomized design with three replications under the growth chamber condition under a controlled environment of 29/22°C (day/night) and 12 h light photoperiod. Then, the treatment plants were exposed to 15/10°C (day/night) cold stress for two weeks and control plants were kept at 29/22°C (day/night). Dry matter accumulation decreased with chilling stress in the two genotypes, with decreases been more pronounced in Hoveizeh genotype. Our results showed that cold treatment increased accumulation of total soluble protein (only in coldtolerant genotype) and proline in rice seedlings, while it decreased the content of chlorophyll, stomatal conductance, total soluble protein (only in cold-sensitive genotype) and dry matter. The results indicated that higher contents of protein and chlorophyll under stress were associated with tolerance to chilling.Key words: Abiotic stress, cold, total soluble protein, proline, total chlorophyll, stomatal conductance

Analysis of vascular development in the hydra sterol biosynthetic mutants of Arabidopsis

Background: The control of vascular tissue development in plants is influenced by diverse hormonal signals, but their interactions during this process are not well understood. Wild-type sterol profiles are essential for growth, tissue patterning and signalling processes in plant development, and are required for regulated vascular patterning. Methodology/Principal Findings: Here we investigate the roles of sterols in vascular tissue development, through an analysis of the Arabidopsis mutants hydra1 and fackel/hydra2, which are defective in the enzymes sterol isomerase and sterol C-14 reductase respectively. We show that defective vascular patterning in the shoot is associated with ectopic cell divisions. Expression of the auxin-regulated AtHB8 homeobox gene is disrupted in mutant embryos and seedlings, associated with variably incomplete vascular strand formation and duplication of the longitudinal axis. Misexpression of the auxin reporter proIAA2:GUS and mislocalization of PIN proteins occurs in the mutants. Introduction of the ethylene-insensitive ein2 mutation partially rescues defective cell division, localization of PIN proteins, and vascular strand development. Conclusions: The results support a model in which sterols are required for correct auxin and ethylene crosstalk to regulate PIN localization, auxin distribution and AtHB8 expression, necessary for correct vascular development