Oligo-carrageenan kappa increases C, N and S assimilation, auxin and gibberellin contents, and growth in Pinus radiata trees
Leaves of tobacco plants var. Burley were sprayed with water (control) or with oligo-carrageenans kappa2 (K), lambda (L), and iota (I) at 1 mg ml−1, once a week, four times in total, and cultivated for 4 months without treatment. Plants treated with K, L, and I showed an increase in leaf biomass of 1.9, 1.8, and 2.5 times, respectively, despite that cellular size was similar in control and treated plants. In addition, net photosynthesis, efficiency of photosystem II and the level of chlorophyll a and b increased in plants treated with oligo-carrageenans. Moreover, the activity of ribulose 1,5-biphosphate carboxylase/oxygenase (rubisco) increased in treated plants, mainly with oligo-carrageenan I, whereas its content did not change compared to control plants. The activity of several NAD(P)H-synthesizing enzymes involved in basal metabolism increased in treated plants, mainly with oligo-carrageenan I. Furthermore, the relative level of transcripts encoding the cell cycle regulatory cyclins A and D and CDKs A and B increased in treated plants, mainly with oligo-carrageenan I. In addition, the amount of ascorbate (ASC) and the activity of ascorbate peroxidase (AP) increased in treated plants, mainly with oligo-carrageenan I, whereas the level of glutathione remained unchanged. Interestingly, the increases in total ascorbate and AP activity linearly correlated with the increase in leaf biomass. Thus, oligo-carrageenans enhanced photosynthesis, basal metabolism, and cell cycle as well as ASC levels and AP activity which may explain, at least in part, the stimulation of plant growth.