Seedlings of maize (Zea mays L. cv WF9 x Mo 17) were grown in vermiculite at various water potentials. The primary root continued slow rates of elongation at water potentials which completely inhibited shoot growth. To gain an increased understanding of the root growth response, we examined the spatial distribution of growth at various water potentials. Time lapse photography of the growth of marked roots revealed that inhibition of root elongation at low water potentials was not explained by a proportional decrease in growth along the length of the growing zone. Instead, longitudinal growth was insensitive to water potentials as low as -1.6 megapascal close to the root apex, but was inhibited increasingly in more basal locations such that the length of the growing zone decreased progressively as the water potential decreased. Cessation of longitudinal growth occurred in tissue of approximately the same age regardless of spatial location or water status, however. Roots growing at low water potentials were also thinner, and analysis revealed that radial growth rates were decreased throughout the elongation zone, resulting in greatly decreased rates of volume expansion.anism by which osmotic adjustment occurs in roots growing at low q. Specifically, our aim is to determine the extent to which the maintenance of lower 4i, in the growing zone under water deficits can be attributed to increased rates of solute deposition, or to reduced growth and hence slower rate of osmoticum dilution by volume expansion. In this paper, attention is focused on the effects of low qf,y on the spatial distribution of expansive growth rate. Although the spatial growth pattern at high q,, for roots of maize and other species has been well characterized for many years (8,11), the extent to which the pattern may change at low q is not known. Indeed, despite early recognition that knowledge of how plant growth patterns may be altered by environmental variation facilitates the opportunities to understand the regulation of the growth response (11), relatively little information of this kind is available. Here, we show that both longitudinal and radial growth patterns are altered markedly in roots growing at low qi,. In a forthcoming paper (RE Sharp, TC Hsiao, WK Silk, unpublished data), we combine this information with profiles of qi5 and component solutes to determine effects of low q on solute deposition rates in the root growing zone, and evaluate the relationship of the growth and solute deposition responses to osmotic adjustment.Plant growth is generally decreased when soil water is limited. Root growth is often less inhibited than shoot growth (2, 21), however. A recent study of maize has shown that root growth is intrinsically less sensitive than growth of the aerial plant parts to low water potentials (q') of the growing region (30), indicating some form of internal regulation. Root elongation is of obvious advantage to plants in drying soil, and may be particularly important for seedling establishment because of the vulnerabi...

We provide an overview of research on climbing plants from Charles Darwin to the present day. Following Darwin's interests, this review will focus on functional perspectives including attachment mechanisms and stem structure and function. We draw attention to a number of unsolved problems inviting future research. These include the mechanism for establishment of the twining habit, a quantitative description following the development of a tissue element through space and time, the chemistry of sticky exudates, the microstructure of xylem and the capacity for water storage, the vulnerability to embolism, and the mechanism for embolism repair. In conclusion we cite evidence that, in response to increasing CO(2) concentration, anthropic perturbation and/ or increasing forest fragmentation, lianas are increasing relative to tree species. In the 21st century, we are returning to the multiscale, multidisciplinary approach taken by Darwin to understand natural history.

Primary roots of maize (Zea mays L. cv WF9 x Mol7) seedlings growing in vermiculite at various water potentials exhibited substantial osmotic adjustment in the growing region. We have assessed quantitatively whether the osmotic adjustment was attributable to increased net solute deposition rates or to slower rates of water deposition associated with reduced volume expansion. Spatial distributions of total osmotica, soluble carbohydrates, potassium, and water were combined with published growth velocity distributions to calculate deposition rate profiles using the continuity equation. Low water potentials had no effect on the rate of total osmoticum deposition per unit length close to the apex, and caused decreased deposition rates in basal regions. However, rates of water deposition decreased more than osmoticum deposition. Consequently, osmoticum deposition rates per unit water volume were increased near the apex and osmotic potentials were lower throughout the growing region. Because the stressed roots were thinner, osmotic adjustment occurred without osmoticum accumulation per unit length. The effects of low water potential on hexose deposition were similar to those for total osmotica, and hexose made a major contribution to the osmotic adjustment in middle and basal regions. In contrast, potassium deposition decreased at low water potentials in close parallel with water deposition, and increases in potassium concentration were small. The results show that growth of the maize primary root at low water potentials involves a complex pattem of morphogenic and metabolic events. Although osmotic adjustment is largely the result of a greater inhibition of volume expansion and water deposition than solute deposition, the contrasting behavior of hexose and potassium deposition indicates that the adjustment is a highly regulated process. leaves (10, 16, 27, 29), stems (11,12,29), shoot apices (15), and roots (7,19,29). It is often observed, however, that root growth is less inhibited than shoot growth at low iJ', (4,19,29 Plant Physiol. Vol. 93,1990 (Table I) were the same as for the measurements of expansive growth distribution described in the preceding paper (20).Osmotic Potential and Solute Contents When the primary roots had attained a length of approximately 5 cm, seedlings were selected for uniformity of root elongation rate (within ± 15% of the mean), as measured by periodically marking under dim light the position of the root apices on the angled Plexiglas face against which they were growing. Preliminary experiments established that both root elongation rate (see Fig. 1 of Sharp et al. [20]) and root tip #, (Fig. 1, inset) were constant with time in all treatments in roots of this length (20-45 h after transplanting, depending on treatment). Adhering vermiculite was removed, and the primary roots were placed on moist (but not wet) graph paper. The apical 0.5 mm was excised to remove a major part of the root cap, and batches of 5 roots were sectioned into 10 1-mm serial segments as measured by ...

Leaves and roots live in dramatically different habitats, but are parts of the same organism. Automated image processing of time-lapse records of these organs has led to understanding of spatial and temporal patterns of growth on time scales from minutes to weeks. Growth zones in roots and leaves show distinct patterns during a diel cycle (24 h period). In dicot leaves under nonstressful conditions these patterns are characterized by endogenous rhythms, sometimes superimposed upon morphogenesis driven by environmental variation. In roots and monocot leaves the growth patterns depend more strongly on environmental fluctuations. Because the impact of spatial variations and temporal fluctuations of above- and belowground environmental parameters must be processed by the plant body as an entire system whose individual modules interact on different levels, growth reactions of individual modules are often highly nonlinear. A mechanistic understanding of plant resource use efficiency and performance in a dynamically fluctuating environment therefore requires an accurate analysis of leaf and root growth patterns in conjunction with knowledge of major intraplant communication systems and metabolic pathways.

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