Increased Proteolysis of Senescing Rice Leaves in the Presence of NaCl and KCl

ASPECTOS CITOMORFOLÓGICOS DO ESTRESSE SALINO EM PLÂNTULAS DE ARROZ (ORYZA SATIVA L.)

RESUMO O objetivo deste trabalho foi realizar um estudo citomorfológico em plantas de arroz submetidas ao estresse salino (170 mM NaCl). Os efeitos da salinidade nas estruturas celulares foram analisados por meio de microscopia óptica e eletrônica de transmissão. Um processo de diferenciação precoce pôde ser observado na planta estressada, porém, o efeito deletério mais drástico foi encontrado nas membranas tilacóides dos cloroplastos. Estes resultados permitiram correlacionar o acúmulo de íons sódio, descritos na literatura, com os efeitos citomorfológicos do estresse salino em tecidos maduros de arroz.

Expression of asparagine synthetase genes in sunflower (Helianthus annuus) under various environmental stresses

In sunflower, asparagine synthetase (AS; EC 6.3.5.4) is encoded by a small family of three genes (HAS1, HAS1.1 and HAS2) that are differentially regulated by light, carbon and nitrogen availability. In this study, the response of each gene to various stress conditions was examined by Northern analysis with gene-specific probes in leaves and roots. The expression of HAS1 and HAS1.1 genes was induced by osmotic stress (300 mM mannitol), salt stress (150 mM NaCl), and heavy-metal stress (20 microM CuSO(4)), more in roots than in leaves. The expression of HAS2 was not significantly altered by stress treatments. The positive response of HAS1 and HAS1.1 genes to osmotic and salt stresses occurred in the light, in contrast to that previously found in unstressed plants. Measurements of sucrose and total free amino acid contents in leaves and roots indicate that the expression of root HAS1 and HAS1.1 genes in stressed plants is not under metabolic control by the intracellular C/N ratio, suggesting the involvement of some specific stress factor(s). Growth of plants at 40 degrees C for 12h negatively affected the expression of HAS1 and HAS1.1 but not that of HAS2.

Heat-inducible rice hsp82 and hsp70 are not always co-regulated

We have characterized several heat-shock-induced genes in rice (Oryza sativa L.) and compared their expression under a variety of conditions. Three of these genes, which are analogs of the hsp82/90 family, lie within a cloned 18-kilobase (kb) region of the genome. The middle member of this cluster, designated hsp82B, has been fully sequenced. The gene uses a promoter containing six putative heat-shock elements as well as several unusual sequence motifs including a stretch of 11 thymidines alternating with 11 adenosines. The mRNA for this gene reaches its highest relative level of expression within 120 min after plants are shifted to 42 degrees C; no other conditions induce this gene. By contrast, we found that during heat stress the expression of hsp70 correlates well with increases in internal ion concentrations, and can also be induced by excess salt or ethanol at normal growth temperatures. These results appear to indicate that whereas hsp70 is induced by all stresses that lead to protein denaturation-including heat stress-HSP82 mRNA accumulates only upon heat stress.