The exogenous application of brassinosteroids to Zea mays (L.) stressed by long-term chilling does not affect the activities of Photosystem 1 or 2
Abstract
The effect of various concentrations of exogenously applied 24-epibrassinolide (E) and 2a,3a,17b-trihydroxy-5a-androstan-6-one (A) on the activities of Photosystem 1 and Hill reaction, the contents of photosynthetic pigments and the growth of plants was examined in young maize plants subjected to long-term chilling stress or grown in normal temperature conditions. Neither the Photosystem 1 nor the Hill reaction activities were in any way affected by treatment of plants with brassinosteroids (BRs), suggesting that the photosynthetic complexes of thylakoid membranes are not the primary site of BRs influence on photosynthesis.
An extremely low (10-14 M) concentration of A applied to the non-stressed plants significantly increased the length of their 4th to the 7th leaves and plant height, as well as the contents of chlorophylls and carotenoids. Under the chilling conditions, this positive effect was significant for the chlorophyll content only and higher concentrations of BRs had usually no effect.