Salinity and drought response alleviate caffeine content of young leaves of Coffea canephora var. Robusta cv. S274

Abstract

With the ever-growing concern of water deficit due to global climatic change, the drought and salinity stress response of plants is a major area of research. However, the effect of these stress on cup-quality of coffee especially, the accumulation of caffeine biosynthetic metabolites, has not been documented. This work studies the methylxanthines (7-methylxanthine, theobromine, caffeine and theophylline) contents in young leaves of coffee in response to PEG-6000 (1.5% and 15% w/v) induced drought and sodium chloride (20mM and 200mM) induced salinity stress. In general, both the stress reduced the caffeine content except for 20mM NaCl. 1.5% PEG reduced caffeine by 0.46 fold and 0.57 fold during first 24hr and 48hr of treatment, respectively; PEG at 15% caused a reduction by 0.36 fold only in the 48hr of treatment compared to untreated plants; and NaCl at 200mM caused a reduction of 0.26 fold and 0.47 fold in the first 24 and 48hrs of treatment, respectively. However 20mM NaCl augmented caffeine by 1.93 and 5.1 fold in the first 24 and 48hrs of treatment, respectively. The levels of caffeine subdued on the withdrawal of the stressor, affirmatively indicating the stress stimuli to be responsible for the observed changes in caffeine levels. The biochemical profile was supported by transcript expression of the caffeine biosynthetic NMT genes and the analysis of regulatory motifs of the promoters. The contents of upstream methylxanthines (7-methylxanthine and theobromine) and the degradation pathway (theophylline) indicate that salinity and drought might have a negative impact on biosynthesis of caffeine but accelerated the rate of caffeine degradation.