Pollen grain expression of osmotic adjustment as a screening method on drought tolerance in several wine and table grape genotypes (Vitis vinifera L.)

Osmotic adjustment is one of the important mechanisms to adapt to drought and it is the only one which is activated under any level of water stress in the plant cells. Grapevine pollen grains response was tested to osmotic stress in fourteen genotypes, initiated by immersion in 55% or 65% polyethylene glycol solutions without and with addition of potassium chloride, to estimate the expressions of osmotic adjustment. The pollen grain test found differences both in the measurements of projected area cytoplasm and expressions of osmotic adjustment present in the cells. Italian Riesling increased pollen grains cytoplasm in PEG solutions with added KCl much more than other genotypes and had the high values for both expressions of induced and overall osmotic adjustment. The results obtained for expression of induced osmotic adjustment underlined the high K accumulation capacity of ‘Italian Riesling’, ‘Burgund mare’ 86 Şt., ‘Muscat d’Adda’ 22 Şt., ‘Muscat Ottonel’ 16 Şt., ‘Pinot gris’ 14 Şt. and ‘Argessis’. The lack of correlation between expressions of induced and intrinsic osmotic adjustment indicated that induced osmotic adjustment expressed by K might use different mechanisms that are activated at the time of water stress with different levels of solute accumulation. Because the accumulation of K in the cells is important in all developmental stages and, in grape yield and quality, pollen responses to induced osmotic adjustment expressed by K could be used as a screening method, for establishing the level of drought sensitivity in the grape varieties under water stress.