Animal anti-apoptotic genes ameliorate the loss of turgor in water-stressed transgenic tobacco

Nicotiana tabacum L. 'Glurk' plants were transformed with antiapoptotic animal genes [chicken Bcl-xl; nematode CED-9; chicken Bcl-xl(GA) a mutant of Bcl-xl; and a 3' non-coding region of human Bcl-2, referred to as 161-1]. Our objectives were to determine whether plant transformation with anti-apoptotic genes ameliorates drought tolerance in tobacco plants by subjecting the plants to a dry-down period. The non-transformed Glurk and the transgenic Glurk harboring G115, which expresses β-glucuronidase, served as controls. Transformation of tobacco plants with animal anti-apoptotic genes significantly impacted the rates of photosynthesis (A) and stomatal conductance (gs), but not to the same extent in every line. Controls generally exhibited higher A and gs than the transformed plants under well-watered conditions. Photosynthesis and stomatal conductance declined significantly on the 3rd day, and approached zero on the 11th day of water deprivation. Differences among controls and transformed tobacco plants disappeared as soil moisture deficit increased. Relative water content (RWC) and leaf water potential (Ψ(w)) remained relatively high in the first 3 d of water deprivation, while a dramatic reduction occurred in all plants on the 6th day. Relative water content did not differ between controls and transformed plants. Water potential declined significantly (became more negative) with the increase in soil moisture deficit. Evident differences among transformed and control plants appeared on the 6th day of water deprivation. The controls, Glurk and G115 generally maintained a higher water potential between days 6 and 11 compared to the transformed tobacco plants. Osmotic adjustment occurred in transformed plants but not in the controls, in response to drought. Relative water content at turgor loss point (RWC(tlp)) and osmotic potential at turgor loss point (Ψ(πtlp)) provided a measure of drought tolerance in plants. G115, Glurk and Bcl-xl plants lost turgor at a higher relative water content than Bcl-xl(GA), CED-9 and 161-1. Ψ(πtlp) in the controls G115 and Glurk were relatively higher compared to the transformed plants. We concluded that transgenic plants with anti-apoptotic genes resulted in moderate amelioration of drought tolerance in tobacco plants.