Translocation, Leaf Distribution, and Nutritional Status of Manganese in Cucumber Plants as Affected by Foliar Application of Exogenous Amino Acids

Abstract

The present study was carried out to investigate the effect of exogenous amino acids (AAs) on leaf apoplastic retention and symplastic absorption, leaf distribution, translocation, and nutritional status of manganese (Mn) in cucumber plants. Results showed that application of AAs increased the symplastic to apoplastic Mn proportion in leaves of cucumber. Furthermore, a greater part of Mn applied with AAs accumulated in the internal area of newly growing leaves suggesting the transport of Mn mostly in the phloem in the presence of AAs. In contrast, Mn preferentially accumulated in the marginal area of treated leaves indicating the Mn movement in xylem according to the transpiration stream. The AAs used in the present study also increased the relative translocation of Mn from treated leaves to the upper leaves and roots. More time was needed for long-distance translocation of Mn from treated leaves to the upper leaves than that to the roots. Application of AAs mainly increased the transport of Mn in the phloem. The leaf PO (peroxidase) activity was the better marker to index the nutritional status of Mn than PPO (polyphenoloxidase) activity. In conclusion, exogenous AAs especially lysine (Lys) promoted the mobility and bioavailability of applied Mn as foliar spray.