Adaptive response of Zillaspinosato different habitats.Wadi Hagoul, Egypt

Abstract

The vegetation in the Wadisis exposed to water stress due to extreme soil water deficits,high temperature and light radiation stress. Plants are unable to dislocate in its own environment therefore they have to cope with various stresses with internal mechanism(s) for the “tolerance” and/or “avoidance”. Zillaspinosa are one of the common plants inhabiting WadiHagoul. Since,Zilla have developed various adaptation mechanisms to provide resistance or tolerance against the harsh environmental conditions. The adaptations of Zillaspinosato dry environmentcan be expressed at four levels: phenological or developmental, morphological, physiological, and metabolic. So, focusing on the strategies to withstand water shortage and light radiation as well as high temperature is the goal of this investigation.Thus, the main experimental results can be briefly summarized in the following: 1-Soil analysis showed a significant decrease in Wadi Hagoul soil moisture particularly at the third location (downstream) during the dry season (August), whereas the EC rises compared with the spring season. However, the pH of the soil remained more or less alkaline throughout the study period and did not seasonally varied significantly. 2- Zilla stems grown under xeric conditions apparently characterized by an increased number of narrow vessels and narrow condensed polyhedral parenchyma forming the pith. The stem was covered with thick cuticle and thick walled epidermal cells as well as the occurrence of suberized subepidermallayeres and interxylarlyschlerenchyma as well as presence of large patches of protophloemfibers. Moreover, the cortex and the pith cells possessed crystals (raphides). Zillastem is photosynthesizing stems in summer and characterized by the presence of green tissues at their periphery. 3-Common traits of desert shrub Zilla leaves are small fleshy whichcharacterized by the occurrence of large condensed mesophyll tissue possesses three to four rows of palisade cells with no intercellular spaces, covered with thick cuticle, thick epidermal cell-walls and two layer of cells forming hypodermis. Moreover, the vascular tissues consist of large number of narrow vessels surrounded by thick walled sclerenchyma. 4- The presented data illustrated that the greatest levels of chlorophyll a and b, a+b, a/b and total carotenoids as well as chlorophylls a+b/carotenoids was measured in Zillaspinosa shoot tops inhabiting the midstream of WadiHagoul bed particularly during the wet spring season.