Developmental mechanisms underlying variable, invariant and plastic phenotypes.

Background: Discussions of phenotypic robustness often consider scenarios where invariant phenotypes are optimal and assume that developmental mechanisms have evolved to buffer the phenotypes of specific traits against stochastic and environmental perturbations. However, plastic plant phenotypes that vary between environments or variable phenotypes that vary stochastically within an environment may also be advantageous in some scenarios.

Scope: Here the conditions under which invariant, plastic and variable phenotypes of specific traits may confer a selective advantage in plants are examined.

Auxin transport through non-hair cells sustains root-hair development.

The plant hormone auxin controls root epidermal cell development in a concentration-dependent manner. Root hairs are produced on a subset of epidermal cells as they increase in distance from the root tip. Auxin is required for their initiation and continued growth, but little is known about its distribution in this region of the root.

The identification of genes involved in the stomatal response to reduced atmospheric relative humidity.

Stomatal pores of higher plants close in response to decreases in atmospheric relative humidity (RH). This is believed to be a mechanism that prevents the plant from losing excess water when exposed to a dry atmosphere and as such is likely to have been of evolutionary significance during the colonization of terrestrial environments by the embryophytes. We have conducted a genetic screen, based on infrared thermal imaging, to identify Arabidopsis genes involved in the stomatal response to reduced RH.

Root gravitropism requires lateral root cap and epidermal cells for transport and response to a mobile auxin signal.

Re-orientation of Arabidopsis seedlings induces a rapid, asymmetric release of the growth regulator auxin from gravity-sensing columella cells at the root apex. The resulting lateral auxin gradient is hypothesized to drive differential cell expansion in elongation-zone tissues. We mapped those root tissues that function to transport or respond to auxin during a gravitropic response.

Micrografting techniques for testing long-distance signalling in Arabidopsis.

Grafting in species other than Arabidopsis has generated persuasive evidence for long-distance signals involved in many plant processes, including regulation of flowering time and shoot branching. Hitherto, such approaches in Arabidopsis have been hampered by the lack of suitable grafting techniques. Here, a range of micrografting methods for young Arabidopsis seedlings are described.

Nitrate and phosphate availability and distribution have different effects on root system architecture of Arabidopsis.

Plant root systems can respond to nutrient availability and distribution by changing the three-dimensional deployment of their roots: their root system architecture (RSA). We have compared RSA in homogeneous and heterogeneous nitrate and phosphate supply in Arabidopsis. Changes in nitrate and phosphate availability were found to have contrasting effects on primary root length and lateral root density, but similar effects on lateral root length.

MAX1 and MAX2 control shoot lateral branching in Arabidopsis.

Plant shoots elaborate their adult form by selective control over the growth of both their primary shoot apical meristem and their axillary shoot meristems. We describe recessive mutations at two loci in Arabidopsis, MAX1 and MAX2, that affect the selective repression of axillary shoots. All the first order (but not higher order) axillary shoots initiated by mutant plants remain active, resulting in bushier shoots than those of wild type.

Ethylene as a Signal Mediating the Wound Response of Tomato Plants.

Plants respond to physical injury, such as that caused by foraging insects, by synthesizing proteins that function in general defense and tissue repair. In tomato plants, one class of wound-responsive genes encodes proteinase inhibitor (pin) proteins shown to block insect feeding. Application of many different factors will induce or inhibit pin gene expression.