THE ROLE OF CATION CHANNELS IN ABIOTIC STRESS RESISTANCE IN RICE

The alarmingly increasing human population needs improved food production but this aim is hampered by different abiotic stresses. Osmotic stress and salt stress are the two prominent examples of abiotic stresses and affect up to 50% of the arable land. These stresses severely affect all plants, but glycophytes (e.g. rice) are especially sensitive. During stress, nutrient uptake, such as K+, is often disturbed. Thus, better K+ nutrition and distribution play a vital role in plant abiotic stress tolerance. To improve K+ nutrition, the role of K+ transporters is likely to be essential. Loss of function and gain of function approaches could help establish the exact function of transporters involved in K+ nutrition. Rice TPKs and AKT1 are K+ channels which are localised to the tonoplast and plasma membrane respectively. The two TPK isoforms, TPKa and TPKb, are localised to the tonoplast of LV and SV respectively. They were characterized in a variety of abiotic stress conditions. The data showed better growth and higher K+ concentration for the TPKa and TPKb transgenic lines when grown in zero K+ and osmotic stress conditions suggesting their role in improving in K+ nutrition. TPKs have no direct involvement in the K+ uptake, but somehow influence K+ uptake and improve K+ nutrition. The higher K+ concentration in the leaves of overexpressor plants suggested the involvement of TPKs in the distribution of K+ within the plant body. TPKs play a role in the guard cells' movements and affect the stomatal conductance and therefore showed a better response to the osmotic stress conditions. The role of rice AKT1 was tested by comparing the knockout and overexpressing lines of AKT1 with the wild type plants. The data suggested that AKT1 is involved in the K+ uptake in a range of external K+ concentrations and osmotic stress conditions. The role of AKT1 is obvious in the K+ deficient conditions where NH4+ is present. The leaf K+ concentration suggested that AKT1 influences K+ transport into the leaves. The K+ concentration in the leaf cells showed an effect on the stomatal conductance and in turn an effect on the growth phenotype under zero K+ and osmotic stress conditions. The data revealed that AKT1 is insensitive to NH4+ toxicity.