Biochemical and physiological changes in the potassium nitrate-induced release of floral bud quiescience in 'Carabao' mango (Mangifera indica L.)

The hypothesis that potassium nitrate induced-ethylene promotes bud break of quiescent mango floral buds through increased gibberellic acid (GA) production which lead to mobilization of starch needed for floral initial growth was investigated. The levels of these metabolites were monitored hourly after the application of potassium nitrate to competent 'Carabao' mango shoots. Likewise, the degree of drooping, flowering response and changes of apical primordium growth were also gathered. Increased ethylene level was observed two hours from spraying nitrate, peaking between 4 to 5 hours and eventually declined thereafter. The total soluble sugars, starch as well as the total non-structural carbohydrates also increased significantly which conincided to ethylene evolution, an indication that demand for carbohydrate is minimal at this time and current photosynthesis is operating due to non-utilization of starch during the early stage of floral development. Mobilization of starch could be observed 8 hours from potassium nitrate spray as exhibited by a decrease of starch level. Coincided to starch decrease was an increase in GA levels both in the shoot apex and leaves which is more than 5-fold and 3-fold, respectively, compared to the control. This is the first such report of GA presence at this developmental stage of the mango floral initial. Overall, the sequence of events leading to apical bud break in potassium nitrate sprayed shoots started from an early rise of ethylene and this was followed by an increase of total soluble sugar and starch 4 hours from KNO3 spray. Increased GA and a concomitant decrease of starch followed after the rise of total soluble sugars and starch. evidence presented also established for the first time that epinasty occurred in 'Carabao' mango which started six days from potassium nitrate spray; coinciding with visible bud break. Since epinasty would be completed only after 18 days and rapid inflorescence development occurs during the same period, the intriguing question of whether structural carbohydrates are utilized to supply the energy requirements of the growing inflorescence emerged as a hypothesis.