Effects of stem-injected plant growth regulators, with or without sucrose,on grain production, biomass and photosynthetic activity of field-grown corn plants

Study of plant growth regulators (PGRs) through conventional foliar applica tion or tissue culture or other organic materials has limitations. No previ ous study has examined the effects of long-term continuous addition of PGRs , with or without sucrose, to field-grown corn (Zea mag's L.) plants. A fie ld study was conducted to determine the effects on corn plant growth and pr oductivity during the grain-filling period of a continuous supply of PGRs, with or without sucrose, using a recently developed injection technique to deliver pressurized solutions through syringe needles sealed to the stem wi th latex. Our four PGRs (IAA, ABA, ethephon and salicylic acid) and a disti lled water control, and two levels of sucrose (150 g l(-1) and a distilled water control) were injected into corn plants for 42 consecutive days durin g the grain-filling period. The plants injected with solutions not containi ng sucrose took up 42 ml more than those injected with sucrose-containing s olutions. Corn plants injected with salicylic acid (SA) produced 9% more gr ain yield than plants injected with no PGRs. The combination of SA and sucr ose increased the photosynthetic rate by 42% when compared with distilled w ater. injection of ethephon resulted in an 11% reduction in grain yield. Ne ither IAA nor ABA altered plant photosynthesis or productivity. Sucrose inj ection increased the dry weight of injected internodes and stover, and indu ced partial stomatal closure, although without any measurable effect on net photosynthetic rate. This study showed that stem injection makes possible the study of changes in plant physiology during grain-filling due to the ef fects of PGRs and metabolites administered continuously over protracted per iods of time. It also demonstrated a previously undocumented stimulation of plant photosynthesis and grain yield by SA.