A study on the germination of five
cultivars exposed to polyethylene glycol-induced water stress indicated that cv Giza 40 showed the highest germination capacity and cv Giza 667 the lowest. The effect of low soil water content was studied on the plant growth, photosynthetic pigment content, organic solutes, relative water content (RWC), lipid peroxidation, membrane stability index (MSI), and the catalase (CAT) and peroxidase (POX) activity in the leaves of 21-day-old
cv Giza 40 and cv Giza 667 plants. With respect to dry weight (DW), drought caused a greater decrease in cv Giza 667 than in cv Giza 40, indicating that cv Giza 40 was more tolerant of low soil water content. Drought decreased the Chl a, Chl b and carotenoid contents and the Chl a/b and carotenoid/Chl a+b ratios in the leaves of cv Giza 667, while in cv Giza 40 a significant increase in these pigment parameters was observed under drought stress. Drought caused a decrease in RWC and MSI and an increase in the lipid peroxidation level and in the catalase (CAT) and peroxidase (POX) activity in both the cultivars, but the decline in RWC and MSI and the increase in lipid peroxidation level in response to drought stress were greater in cv Giza 667 than in cv Giza 40. The CAT and POX activities were higher in Giza 40 than in Giza 667 under both control and drought conditions. Drought induced the accumulation of soluble sugars, soluble proteins, free amino acids and proline in both cultivars. However, this accumulation was lower in cv Giza 667 than in the more tolerant cv Giza 40. These results indicate that cv Giza 40 showed better protection against drought-induced oxidative stress through higher CAT and POX activities and osmolyte concentrations than cv Giza 667.