Effect of seasonal drought and cactus X virus infection on the crassulacean acid metabolism ofAgave sisalanaplants growing in a neotropical savanna

Abstract

Healthy and cactus X virus-infected Agave sisalana plants were collected during the dry and rainy seasons in two contrasting savanna sites. At site 1, the soil water content showed no seasonal variations, but at site 2 it was much lower during the dry season than in the rainy season. When compared to healthy plants (HP), virus infection reduced the total leaf area, the Δ of titratable acidity and the water content of the plants, regardless of the season. In virus-infected plants at site 1 (VIP-1) the magnitude of the effect elicited by the virus did not differ between seasons, whereas, in virus-infected plants at site 2 (VIP-2) the deleterious effect of the virus was more pronounced during the dry season. In the dry season, VIP-1 and VIP-2 accumulated more fructans along the diurnal cycle and had higher net diurnal carbon gain than HP, with higher values in VIP-2. With the onset of rain the total leaf area of VIP-2 increased and the Δ of titratable acidity and water content reached the values seen in VIP-1. During the rainy season there was less accumulation of fructans and the net diurnal carbon gain was lower in both VIP-1 and VIP-2 compared with HP, with VIP-2 showing the lower values. In VIP-1 and VIP-2 there was also a marked reduction in the diurnal accumulation of α-amino-N at both seasons. The data obtained in young developing leaves allowed us to discuss the present data in terms of alterations in the plants sink/source ratio caused by drought and cactus X virus infection