SUCROSE - A SOLUTE THAT ACCUMULATES IN THE GUARD-CELL APOPLAST AND GUARD-CELL SYMPLAST OF OPEN STOMATA

Stomatal conductances of Yicin faba leaves were recorded over a day, C oordinately, (a) guard cells dissected from leaflets were assayed, pro viding total sucrose content, and (b) guard cells dissected from rinse d epidermes were also assayed, providing symplastic sucrose content, C ompared with that of pre-dawn samples, apoplastic sucrose content incr eased 4.8-5.2x (2 experiments), reaching 1,130-1,300 fmol . guard-cell -pair(-1) at midday, when conductance was highest (ca, 0.13 mol . m(-2 ) . s(-1)); symplastic sucrose content increased 2.5-3.5x, reaching 35 0-390 fmol . guard-cell-pair(-1). Thus, there is a correlation between transpiration and guard-cell sucrose content, particularly that porti on localized to the apoplast, Moreover, apoplastic sucrose is apparent ly a source of guard-cell nutrition and, possibly, osmoticum.