Gas Exchange and Leaf Ultrastructure of Tinnevelly Senna, Cassia angustifolia, under Drought and Nitrogen Stress

Abstract

sain et al., 1984;Lemli, 1986; Folkard, 1995, p. 352). The primary active constituents of senna are two rhein-Choice of crops is limited in dry agro-ecosystems. Senna, Cassia dianthrone-8,8Ј diglucosides called sennoside A and B.angustifolia Vahl, a tropical medicinal plant, has potential as a dryland crop. This study was conducted to investigate gas exchange and leaf Despite the availability of some synthetic products, surface ultrastructural responses of senna to drought and foliar-applied sennoside formulations are increasingly used as safe nitrogen under greenhouse conditions. Drought was imposed cycli- laxatives (Atzorn et al., 1981; Al-Dakan et al., 1995). cally as four, 1-wk spells by withholding water. Additional nitrogen Senna, however, has not received wide recognition as was provided as a foliar treatment of 1% (w/v) urea at the end of a crop in many countries except for India where it is each of first three drought cycles. Drought-stressed plants had the grown in arid, nutrient-poor, sandy soils (Pareek et al., same net photosynthesis (P net ) as well-watered plants until the leaf 1983). Preliminary on-farm observations in the dry zone water potential dropped below approximately Ϫ0.8 MPa. Leaf water of Sri Lanka indicated that senna can be successfully potential of approximately Ϫ2 MPa completely suppressed P net . Foliar planted as an unirrigated crop on alfisols in the dry nitrogen treatment increased P net Ͼ 30% in both water-stressed and season, if the residual moisture from the previous wet well-watered plants. Intrinsic water use efficiency was unaffected by cyclic drought. Leaf area per plant increased 156% because of foliar season is used for early plant establishment. Furthernitrogen treatment in well-watered plants but remained unchanged more, senna plants can be grown by seedlings, ratooning in drought-stressed plants. Stomatal count per leaflet decreased 25% (pruning seedling plants near the base and allowing or more because of drought regardless of foliar nitrogen treatment regrowth) and cuttings. We previously reported the efon either abaxial or adaxial leaf surface. Foliar nitrogen treatment fects of environmental conditions, propagation methdecreased adaxial but increased abaxial stomatal count regardless of ods, and cultural practices on the concentrations of sendrought treatment. Trichome count was more than eight times greater nosides in dried senna leaves, the main harvest product on the abaxial than the adaxial leaf surface under any treatment of senna (Ratnayaka et al., 1998). The primary objective combination. Adaxial trichome number increased under drought, but of this study was to investigate the impact of drought decreased under nitrogen treatment. Abaxial trichome count inand foliar nitrogen application (as urea) on gas exchange creased because of drought only in plants deprived of nitrogen treatment. Maintenance of high carbon gain and water use efficiency, and some leaf surface characteristics of senna toward drought deciduousness, and plasticity in stomatal and trichome ...

Developmental Stage Specificity and the Role of Mitochondrial Metabolism in the Response of Arabidopsis Leaves to Prolonged Mild Osmotic Stress

“…Stress not only affected final leaf size but also the SI, resulting in decreased stomatal density, which can be interpreted as an adaptation to minimize water loss. Ratnayaka and Kincaid, 2005). While the number of stomata decreased, trichome density increased.…”

Reduction of drought stress effect in spring barley (Hordeum vulgare L.) by nitrogen fertilization

“…plants showed that N (in the form of urea) applied on leaves in the vegetative stage of growth at the end of the plant dehydra-tion period (Ψw = -2 MPa) increased the net CO 2 assimilation by 30%, compared with the plants exposed only to water dehydration. The plants treated with high N under water stress reduced leaf area but kept their abaxial stomata open; it led to maintaining the CO 2 availability for assimilation and consequently to WUE (water use efficiency) enhancement (Ratnayaka and Kincaid 2005). In various examined crop species, NRA was often shown to decline due to water stress (Dubey and Pessarakli 1995).…”

Atmospheric humidity and genotype are key determinants of the diurnal stomatal conductance pattern

“…Higher g s and Tr , in terms of absolute values, are associated with better performance of tolerant genotypes under stress conditions (Bota, Flexas, & Medrano, ; Saeidi & Abdoli, ). The ability to maintain high carbon gain confers stress tolerance in crops (Ratnayaka & Kincaid, ). Drought tolerant Jinmai 47 is capable of keeping higher g s for carbon assimilation under LRH and largely enhancing g s under HRH, thus stably gain higher yield in the drier rain‐fed area.…”