ABSTRACT
Free putrescine levels remained higher in the ultraviolet (UV)-B treated shoots than in the controls throughout the 14 days of the experiment. S. Predieri et al. worked on the influence of UV-B radiation on polyamines in pear shoots. Conjugated putrescine levels were very low and were unaffected by UV-B exposure. The accumulation of putrescine appeared to be an early response to UV-B stress. The chapter focuses on radiation stress, considering the effects of shade/low light intensity as it results during an overcast sky, cloudiness or under story farming/dense community; intense sunshine occasioned in hot summer months; and the effects of UV-B radiation common at higher altitudes, and the possibility of its increase with depleting ozone layer. The positive correlation between 1-aminocyclopropane-l-carboxylic acid (ACC) and ethylene indicates that ethylene production under low light intensity stress may be controlled by regulating synthesis of ACC. Cytokinin, auxin and sugar contents of the hypocotyl and thickening growth rapidly increased under high light intensity.
