Different Pathways are Involved in the Enhancement of Photosynthetic Rate by Sodium Bisulfite and Benzyladenine, a Case Study with Strawberry (Fragaria×Ananassa Duch) Plants

In order to understand the pathway involved in the chemical enhancement of photosynthetic rate, sodium bisulfite (NaHSO3) and benzyladenine (BA), a growth regulator, were applied to strawberry plants. The influence of these compounds on gas exchange and millisecond delayed light emission (ms-DLE) was investigated using 2-month-old plants. Results showed the net photosynthetic rate (A) in leaves was promoted by both NaHSO3 and BA. Stomatal conductance (g) and transpiration rate (E) were significantly increased only by BA, while intercellular CO2 concentration (Ci) was significantly decreased by NaHSO3. The enhancement of A by NaHSO3 and BA was only a short-term effect, lasting approximately 5 days for NaHSO3 and 30 h for BA. Plants treated with NaHSO3, BA or NaHSO3 + BA, showed no significant fluctuations in carboxylation efficiency (CE), photorespiration (RP) or dark respiration (RD). These results suggest that the influences of NaHSO3 and BA on gas exchange particularly A, could be via different mechanisms: the enhancement of A by the application of low concentrations of NaHSO3 appears to be associated with increased cyclic electron flow, while BA enhancement of A is at least partially due to increased g and/or E.