Nucleus and nucleolus in pea root meristems are affected by variations in moisture content

This paper examines the morphological and biochemical variations occurring in the nucleus when considerable changes in moisture content take place in the tissue. The tissue used for this investigation was the root meristem of Pisum sativum L. at three different developmental stages: during seed maturation, during seed germination and during a vegetative stage. These different developmental stages were representative of three different degrees of moisture content. Seed maturation represented the case of tissue undergoing desiccation whereas seed germination represented the case of tissue undergoing hydration. PEG-treated seedlings represented the case of a vegetative tissue subjected to water stress. The data demonstrated that when moisture content in root meristems was low, the nucleus underwent a reduction in diameter and a change in chromatin arrangement. The nucleolus shrank considerably in diameter and became less visible. These events were simultaneous to qualitative and quantitative variations in the nuclear protein pattern. The relationship between morphological and biochemical events is unknown. However, when the moisture content in the tissue was low, the cell cycle in meristematic cells was arrested in G1 and G2 phases in the case of seed maturation. In water- stressed seedlings the cell cycle was arrested in late S or earlv G1 phase. The differences observed between natural desiccation and artificially induced water stress could be due to the different rate of water loss from tissues. This paper reports for the first time the presence of Dehydrins in nuclei of higher plants. These proteins undergo quantitative variations related to changes in the moisture content of the tissue. The hypothesis of a possible role of Dehydrins in protecting DNA is discussed.