The present study was undertaken to investigate the changes induced by chilling on fatty acid composition of tonoplast vesicles from hypocotyls of Vigna unguiculata (L.) Walp. The 7 day-old control seedlings were grown at 25°C while treated seedlings were submitted to low temperatures (10°C and 4°C) for 4 days after 3 days germination. The chilling stress resulted in a differential inhibition of plant growth at 10°C and 4°C. Following chilling at 10°C and 4°C, the rate of unsaturated to saturated fatty acids increased under chilling stress. Our results suggest that the increase of unsaturated fatty acids content as well as the higher rate unsaturated/saturate fatty acids might be used by V. unguiculata plants as an adaptation mechanism likely to maintain the vacuolar membrane fluidity under low temperatures.Key words: chilling, cowpea, lipid, fatty acids, membrane, vacuole. resuMoO presente trabalho analisa as mudanças na composição de ácidos graxos de vesículas de tonoplato de hipocótilos de Vigna unguiculata (L.) Walp induzida por estresse causado por baixas temperaturas. Plântulas em condição controle desenvolveram-se por 7 dias à temperatura de 25°C e as plântulas tratadas foram submetidas a 10 ou 4°C por 4 dias, 3 dias após a germinação a 25°C. O frio (10 ou 4°C) induziu um efeito inibitório no desenvolvimento das plântulas e esse efeito foi mais pronunciado a 4°C. Além disso, o grau de insaturação dos ácidos graxos nas vesículas de tonoplasto aumentou sob o efeito do frio, o que pode indicar um aumento da permeabilidade das vesículas da membrana vacuolar. Nossos resultados sugerem que plantas de V. unguiculata aumentaram o seu conteúdo de ácidos graxos insaturados bem como a razão entre ácidos graxos insaturados/saturados, como mecanismo de adaptação ao frio numa tentativa de manter a fluidez da membrana vacuolar.

Lead (Pb) is one of the most toxic anthropogenic pollutants, occurring widely in both terrestrial and aquatic ecosystems, where it impairs plant growth and development. In this work, the effect of 0.5 mM EDTA-Pb was evaluated in two Vigna unguiculata cultivars (SV and SET), with the aim of detecting genotype/cultivar dependent changes in the physiological and anti-oxidant responses (CAT and APX) of a leguminous plant. The data showed that SV accumulated more Pb in roots while SET accumulated more in leaves, indicating differential regulation in Pb-translocation/accumulation. Lead affected the growth of SV less severely than SET, mainly associated with reduced inhibition in photosynthetic parameters. Furthermore, CAT and APX activities increased or were sustained at elevated levels in both cultivars in response to lead. However, gene expression analyses revealed that CAT1 was the main lead responsive gene in SET while CAT2 was more responsive in SV. APX1 was higher expressed in tissues with higher Pb-accumulation while APX2 was ubiquitously responsive to lead in both cultivars. Taken together, these results reveal differential ability of V. unguiculata cultivars in Pb-accumulation in different tissues affecting distinctly physiological and anti-oxidant responses. In addition, the existence of cultivars with predominant Pb-accumulation in aerial tissues invokes a need for studies to identify pollution-safe cultivars of leguminous plants to ensure food safety.

Vigna unguiculata (cowpea) is a legume adapted to high temperatures and is sensitive to low temperatures. Temperature is one of the limiting factors of growth and yield for many crops but its effect on cowpea metabolism is not known. We investigated the effect of chilling on activity of vacuolar proton pumps (V-ATPase and V-PPase) and their protein content in tonoplast vesicles of cowpea hypocotyls. Seedlings grown for 7 days at 10 or 4°C were used for experiments. Chilling treatment at 10 or 4°C markedly suppressed growth of cowpea seedlings. Following chilling at 10 and 4°C, activity of both proton pumps and the relative amount of V-PPase and subunit A of V-ATPase were significantly increased. Both substrate hydrolysis and H ? transport activities of V-PPase remained at relatively high levels during chilling treatment. For V-ATPase, treatment at 10°C for 6 days increased the ATP hydrolysis activity. However, the H ? transport activity of the enzyme was increased when treated for 4 days but was markedly decreased when treated for 6 days. Our results provide evidence for different regulation for these vacuolar proton pumps, indicating that V-PPase is the more stable proton pump throughout chilling stress.