Phenolics metabolism in boron-deficient tea [Camellia sinensis (L.) O. Kuntze] plants.

Modification in the metabolism of phenolic compounds under boron (B) deficiency conditions was studied in tea plants. Plants were grown from seed, treated with low B in hydroponic medium under environmentally controlled conditions for six weeks. Dry matter production and B content of plants were significantly declined under B deficiency conditions. Boron starvation resulted in rising phenylalanine ammonia lyase activity in the young leaves and declining polyphenol oxidase activity in the roots. Soluble phenolics fraction was increased up to 3.4-fold in the young leaves while did not influence by B nutrition in the old leaves and roots. Cell wall (CW) bound phenolics and lignin content was lower in B-deficient plants compared with B-sufficient ones. Boron deficiency increased significantly activity of soluble peroxidase (POD) only in the leaves. Activity of ionically bound POD was decreased in the old leaf and roots while it increased in the young leaves upon B deprivation. Activity of covalently bound POD decreased in the roots and leaves of different age in low B plants. Our results suggested that tea plant is highly tolerant species to B deficiency and CW tightening and accumulation of oxidized phenolics are not mechanisms for growth inhibition under B deficiency conditions.