The Role of DNA Synthesis During Hypocotyl Elongation in Light and Dark

Fluorodeoxyuridine, an inhibitor of DNA synthesis, did not affectgermination and post-germinative growth in the aerial part oflettuce and Haplopappus gracilis seedlings when grown in thelight. In the dark, however, elongation of the hypocotyl wasinhibited by fluorodeoxyuridine, strikingly in lettuce and onlyslightly in Haplopappus gracilis. This could imply that thecontrolling mechanism of hypocotyl elongation is in some casesrelated to DNA synthesis, either because mitotic processes (oftenlittle taken into account in considering hypocotyl growth) areinvolved in the elongation of hypocotyls only when they aregrown in the dark, or because DNA synthesis affects cell elongationdirectly, or through the production of a greater number of endopolyploidcells in the dark. Using mainly autoradiographic and cytofluorimetricmethods, these possibilities were tested. Besides lettuce (Lactucasativa L. var. Great Lakes) and H. gracilis (Nutt.) Gray, radish(Raphanus sativus L. var. Tondo rosso quarantino) and soybean(Soya hyspida Sieb. and Zucc. var. Tokyo) seedlings were alsostudied. Fluorodeoxyuridine drastically inhibits cell elongation onlywhen it is preceded or accompanied by mitotic or endomitoticevents. Need for DNA synthesis during hypocotyl elongation,as well as during early post-germinative growth, seems to beof particular importance when endomitotic processes are involved. DNA synthesis, elongation, endoreduplication, fluorodeoxyuridine, Haplopappus gracilis (Nutt.) Gray, Lactuca sativa L., Raphanus sativus L., Soya hyspida Sieb and Zucc     

Water Stress and --SH-Dependent Physiological Activities in Young Maize Plants

In young maize plants, water stress affects the —SH-dependentactivities: photosynthesis and dark respiration are reducedto about 60% at the wilting point; protein synthesis is inhibitedeven by moderate stress; and nitrate reductase activity is immediatelyinhibited also, prior to significant changes in the water statusof the plant As protoplasmatic protein denaturation occurs,protein —SS—increases at the expense of —SH,with consequent decrease of the —SH/—SS— ratio.The linear correlation between —SH/—SS— ratioand —SH-dependent activities suggests a strict dependencebetween them. A moderate increment both in rhodanese activityand labile sulphide content has been also demonstrated at thebeginning of the stress.     

Water Deficit in Pea Root Tips: Effects on the Cell Cycle and on the Production of Dehydrin-like Proteins

Dehydrin-like proteins have been detected in nuclei and cytoplasmof meristematic root tip cells from pea seedlings subjectedto slow dehydration at 90% relative humidity for 48 h or more.Evidence was gained from Western blotting and immunocytochemicalexperiments using an antibody raised against the conserved domainof dehydrin proteins. Flow cytometer analysis has shown thatcycling cells of root tip meristems from dehydrated seedlingsare mostly arrested in G2 phase. Other stress treatments thoughtto involve water depletion (osmotic stress, cold treatment)or to modulate cell response to water deficit (abscisic acid)gave less clear-cut results with all treatments lowering theproportion of cells entering the S phase, but without a definiteand persistent arrest in any preferential phase of the cycle.Possible interrelationships between G2 arrest and dehydrin productionare discussed. Cell cycle; dehydrins; flow cytometry; nuclei; pea; Pisum sativum L.; water stress