Effects of Low Water Potential on Cortical Cell Length in Growing Regions of Maize Roots

Abstract

Roots growing under low water potential commonly exhibit a marked decrease in growth rate and in diameter. Using median longitudinal sections of fixed maize (Zea mays L. cv WF9 x Mo 17) seedling roots, we investigated the cellular basis for these effects. Cortical cells in the shortened elongation zone of water stressed roots were longer than cortical cells in the comparable location of well-watered roots. Nearly twofold differences in cell length were seen in the region 2 to 4 millimeters behind the root apex. The shortened growth zone, however, leads to a final mean cortical cell length approximately 30% shorter in the stressed roots. These differences were present regardless of the age of the control roots. These data, and the slower growth rate seen in water-stressed roots, suggest that the water deficit causes a significant reduction in the rate of cell supply to the cortical cell files.We have investigated the anatomical basis for the altered growth patterns seen in response to water stress. It is well known that corn roots growing under conditions of severe water stress exhibit a much slower root extension rate than that seen in well-watered corn (6,13,17 Upon harvesting, the overall length of the roots was measured, and the apical 15 mm was excised and placed in 2.5% glutaraldehyde in 0.1 M potassium phosphate buffer (pH 7.0) overnight at room temperature. After three 15 min washes in buffer, the root apices were dehydrated in ethanol (10%, 25%, 50%, 70%; 30 min each) and stored in 70% ethanol at 4°C. The roots were dehydrated further in 95% ethanol before infiltrating. Infiltrated roots were cut and embedded as 7.5 mm segments in glycol methacrylate (Historesin, LKB-Produkter). Serial longisections were cut at 3 ,um intervals on a JB-4 microtome, and stained with toluidine blue 0 at 60°C (15). Median sections were photographed with Kodak Panatomic-X film.For transverse sections, only the apical 10 mm of the root was originally excised prior to fixation. Later, thin slices of tissue were cut 2.5 and 5.5 mm behind root apices for use in cutting transverse sections. All other procedures were the same as for the longisections.Root extension rates were calculated from initial and final root lengths over the growth period. Cell Size DataCortical cell lengths were measured on prints made from 35 mm negatives. Every 0.25 mm along the root, cell size measurements were made of the five "middle" cortical cell files on each of five to seven roots. The same five files were used for all the measurements whenever possible, but occasionally one or more of the cell measurements at a given point needed to be taken from the corresponding region on the opposite side of the stele. Cell size at each point was taken as an average of these 25 to 35 cells. Overall cell diameter was also measured at each point.

Root growth, developmental changes in the apex, and hydraulic conductivity for Opuntia ficus‐indica during drought

“…At 14 d of gradual drying, the length of fully elongated cells was less than under wet conditions. In other species, cell elongation is also suppressed under water stress, and the length of the root elongation zone decreases (Sharp et al, 1988 ;Fraser, Silk & Rost, 1990 ;Spollen & Sharp, 1991). Partly as a consequence of the cells being 30 % shorter, at 14 d of gradual drying the length of the elongation zone for O. ficus-indica was reduced by 69 %.…”

Endosperm Cell Division in Maize Kernels Cultured at Three Levels of Water Potential

“…In many plant tissues, elevated osmoticum levels or water deficit decrease the rate of cell division (3,5,16,20,22). Although cell expansion rates also decreased in several of these cases (5,16,20), the magnitude of treatment effect on cell division versus cell expansion depended on the timing of treatment application with respect to developmental events (20,22). In the current study, kernels were transferred to osmoticum treatments at 5 DAP, which was shortly before the period of most rapid cell division (Fig.…”

Temperature Affects Expansion Rate of Maize Leaves without Change in Spatial Distribution of Cell Length (Analysis of the Coordination between Cell Division and Cell Expansion)

“…The cell flux vm) in the mature zone was calculated (Fraser et al, 1990) as the ratio of LER to mature cell length (Am):…”

“…In such a case, measuring the proportion of cells currently in mitosis at a given time is not sufficient for assessing cell division rate. Observed proportions depend, in addition to division rate, on cell displacement rate (Fraser et al, 1990) and are therefore difficult to interpret if measured alone. We performed spatial analyses of leaf elongation and cell division in plants grown in the growth chamber, where meristem temperature can be kept constant, thereby maintaining cell flux Plant Physiol.…”