This study aims to explain the effects of silicon on chlorophyll and to measure gas exchange and carbohydrate levels in two Lycopersicon esculentum cultivars that are exposed to drought. The experimental design used in this study was a randomised combination of five different water and silicon conditions (control, water deficit + 0.00 μmol Si, water deficit + 0.25 μmol Si, water deficit + 1.00 μmol Si, and water deficit + 1.75 μmol Si) applied to the two cultivars (Super Marmante and Santa Cruz). Parameters measured were gas exchanges, chlorophylls, and total soluble carbohydrates. Silicon at concentrations of 0.25, 1.00, and 1.75 μmol induced a gradual increase in the total chlorophyll levels. A correlation analysis revealed a linear, positive interaction between the leaf water potential and the total chlorophyll (r = 0.71; P < 0.05). This study confirmed the hypothesis that silicon has a beneficial effect with regard to chlorophyll. Under water-deficient conditions, both cultivars showed an increase in chlorophyll a when treated with silicon in addition to changes in the total chlorophyll levels. These results were supported by the change in leaf water potential. In addition, a reduction of the effects of water restriction was also observed in the transpiration rate, the stomatal conductance and in the levels of total carbohydrates.

No abstract

Because of their high commercial value and international market acceptance, mahogany species have been indiscriminately explored even in protected areas, resulting in extinction threat. In this study, we aimed to assess the physiology of young plants of Brazilian (Swietenia macrophylla (King)) and African (Khaya ivorensis A. Chev.) mahogany regarding their drought tolerance. The species analyzed showed different responses in the behavior of variables in the two periods studied. The highest values of stomatal conductance (gs) and transpiration (E) were observed in the rainy season because of excess of soil water; while in the dry season, deficit of soil water caused gs reduction of 90% in 2006 and 75% in 2007, and E reduction of 80% and 60%, respectively, for the same periods. The dry season, with lower values of leaf water potential and leaf relative water content, induced higher levels of sucrose, proline and total soluble amino acids compared to the rainy season, indicating emergence of the mechanism of osmoregulation in the studied species. 90%, em 2006, e em 75%, em 2007; de E, observaram- RESUMO: As espécies de mogno, por seu alto valor comercial e aceitação no mercado internacional, têm sido exploradas de forma indiscriminada, mesmo em áreas protegidas, acarretando ameaça de extinção. O objetivo deste trabalho foi estudar a fisiologia de plantas jovens de mogno brasileiro [Swietenia macrophylla (King)] e africano (Khaya ivorensis A. Chev.) quanto à tolerância à seca. As espécies apresentaram diferentes respostas no comportamento das variáveis, nas duas épocas estudadas. Os maiores valores de condutância estomática (gs) e transpiração (E) foram observados na época chuvosa, em virtude do excedente hídrico do solo, enquanto que, na época seca, a deficiência hídrica promoveu redução de gs em

The aim of this study was to investigate the changes in photosynthetic pigments and carbohydrate contents on resistant and susceptible plants of Phaseolus vulgaris L. (cvs. Mexico 222 and Widusa) infected by Colletotrichum lindemuthianum race 23. The experimental design used was entirely randomized in factorial scheme, with 2 cultivars (Mexico 222 and Widusa) and 2 treatments (control and inoculated). The cultivar Widusa (susceptible) showed a significant reduction in photosynthetic pigments, and an increase in the total carbohydrates, sucrose and reducing carbohydrates, whereas the cultivar Mexico 222 (resistant) showed a significant change in the carotenoid and total carbohydrate contents.

No abstract