Photosynthetic Carbon Metabolism in the Palisade Parenchyma and Spongy Parenchyma of Vicia faba L.

Abstract

Palisade parenchyma cells and spongy parenchyma cells were isolated separately from Vicia faba L. leaflets. Extracts of the cell isolates were assayed for several enzymes involved in CO2 fxation and photorespiration. When compared on a chlorophyll basis, the levels of enzyme activities either were equal in the different cell types or were greater in the spongy parenchyma; this difference is a reflection, perhaps, of the higher protein-chlorophyll ratio in the latter tissue. The distribution of radioactivity in the products of photosynthesis by each cell type was the same at various times after exposure to NaH'4CO3, and the kinetics of 14C incorporation into these compounds was similar. However, a larger percentage of radioactivity was incorporated by the cell isolates into the 80% ethanol-insoluble fraction and correspondingly less into the neutral fraction as compared to whole leaf. It was concluded that photosynthetic CO 2fxation is similar in the different mesophyll tissues from which these cells were derived.Compartmentation of photosynthetic processes between the mesophyll and bundle sheath cells of C4 plants has been partially elucidated (6,15 The kinetic data of 14C incorporation into glycine and serine were markedly different in extracts of shavings taken from the upper ("palisade") and lower ("spongy") surfaces of frozen coltsfoot leaf which had been exposed to '4C02 before freezing (22). Outlaw and Fisher (25) found that the percentage of '4C in ths combined glycine and serine fraction from extracts of microtome sections of palisade parenchyma after pulse-labeling a Vicia faba leaf was smaller than in sections of spongy parenchyma. Moreover, differences in the internal organization of microbodies from the different mesophyll cell types have been observed (9). These observations suggest the possibility of differences in photorespiration. We have isolated palisade parenchyma cells and spongy parenchyma cells from V. faba leaflet, and determined levels of certain enzyme activities involved in photosynthetic carbon metabolism and the kinetics of photosynthetic '4C incorporation into various compounds. MATERIALS AND METHODSPlant Material. V. faba L. plants were grown on Hoagland solution in a soil-vermiculite mixture in a growth cabinet, set on a 14-hr day at 21 C and 15 C at night. Irradiance from incandescent and fluorescent bulbs was 4000 ft-c at plant level.Cell Preparation. Young, fully expanded leaves were used from 3-to 5-week-old plants. About 2.5 g of leaflet, from which the lower epidermis had been stripped, were placed in a 125-mi side arm flask and vacuum-infiltrated (300 mm Hg, minimum pressure) with 20 ml of maceration medium. The medium was similar to that used by others (7, 17, 32) and contained 0.8 M sorbitol, 20 mm K2SO4, 1 mm KNO3, 0.2 mm KH2PO4, 0.2 mM MgSO4, 1 mM CaC12, 1 ,M KI, 0.01 MM CuSO4, 300 ug/ml Cephaloradine (E. Lilly). The medium was adjusted to pH 5.8 before adding 1% (w/v) Macerase (Calbiochem). The stripped leaflets were incubated at 30 C in this solution on a shak...

Plant, cell, and molecular mechanisms of abscisic-acid regulation of stomatal apertures. A new mechanism for the regulation of stomatal-aperture size in intact leaves: Accumulation of mesophyll-derived sucrose in the guard-cell wall of Vicia faba L.

“…Those data comprised entire kinetics series of suc specific radioactivities for different suc pools of several individual lean ets; thus, the resulting separate curves were each derived from individual leaflets that served as internal controls for the rate of I4C incorporation (see . In the present experiments (including those not shown), the rates of I4C incorporation (soluble fraction) by palisade cells of different leaflets also varied somewhat (equivalent to 86 k 30 (SE) pmol COrmg-' chl-hr", compared with a reference value of 20 to 60 pmol CO2.rng-l chl-hr-' for enzymically isolated mesophyll cells of K fuba (Outlaw et al, 1976)). This rate of photosynthesis is -14 pmol COrcell~'-hr" (conversion factors collected in Outlaw et al, 1985) or 1.3 pmol C02.cm-2 leaf areahr" (27 mg fiesh leafkme2 leaf area, unpublished).…”

A New Mechanism for the Regulation of Stomatal Aperture Size in Intact Leaves (Accumulation of Mesophyll-Derived Sucrose in the Guard-Cell Wall of Vicia faba)

“…Thus, on a cell-volume basis, the rate of photosynthesis in V . faba palisade cells is approximately 2-fold that of spongy cells at the experimental PAR (Outlaw and Fisher, 1975b), but the protein-to-chlorophyll ratio in palisade cells is approximately 0.5-fold that of spongy cells (Outlaw et al, 1976). Our method of conversion (86 pmol CO, mg-l chlorophyll h-' and 27 mg fresh leaf cm-' leaf area, S.Q.…”

“…SE). This rate of incorporation is equivalent to 86 pmol CO, mg-l chlorophyll h-' (conversion factors from Outlaw et al, 1985), which may be compared with a reference value of 20 to 60 pmol CO, mg-' chlorophyll h-' for enzymically isolated mesophyll cells of V. fubu (Outlaw et al, 1976).…”

Stomatal Behavior and CO2 Exchange Characteristics in Amphistomatous Leaves

“…These data, plus consideration of the anisolateral nature of the mesophyll in many C3 dicotyledonous species, raise the possibility that different CO2 exchange characteristics may exist for CO2 entering through one surface or the other, caused by either differences in resistance to CO2 diffusion through the intercellular spaces or differences in photosynthetic characteristics between palisade and spongy mesophyll cells. Although differences in carbon metabolism between these two types of cells have been shown not to exist (7), differences in electron transport reactions are indicated by differences in fluorescence characteristics between upper and lower surfaces of leaves (1).…”