The reproductive (gametophytic) phase in flowering plants is often highly sensitive to hot or cold temperature stresses, with even a single hot day or cold night sometimes being fatal to reproductive success. This review describes studies of temperature stress on several crop plants, which suggest that pollen development and fertilization may often be the most sensitive reproductive stage. Transcriptome and proteomic studies on several plant species are beginning to identify stress response pathways that function during pollen development. An example is provided here of genotypic differences in the reproductive stress tolerance between two ecotypes of Arabidopsis thaliana Columbia (Col) and Hilversum (Hi-0), when reproducing under conditions of hot days and cold nights. Hi-0 exhibited a more severe reduction in seed set, correlated with a reduction in pollen tube growth potential and tropism defects. Hi-0 thus provides an Arabidopsis model to investigate strategies for improved stress tolerance in pollen. Understanding how different plants cope with stress during reproductive development offers the potential to identify genetic traits that could be manipulated to improve temperature tolerance in selected crop species being cultivated in marginal climates.

White lupin (Lupinus albus) adapts to phosphorus deficiency (ϪP) by the development of short, densely clustered lateral roots called proteoid (or cluster) roots. In an effort to better understand the molecular events mediating these adaptive responses, we have isolated and sequenced 2,102 expressed sequence tags (ESTs) from cDNA libraries prepared with RNA isolated at different stages of proteoid root development. Determination of overlapping regions revealed 322 contigs (redundant copy transcripts) and 1,126 singletons (single-copy transcripts) that compile to a total of 1,448 unique genes (unigenes). Nylon filter arrays with these 2,102 ESTs from proteoid roots were performed to evaluate global aspects of gene expression in response to ϪP stress. ESTs differentially expressed in P-deficient proteoid roots compared with ϩP and ϪP normal roots include genes involved in carbon metabolism, secondary metabolism, P scavenging and remobilization, plant hormone metabolism, and signal transduction.Phosphorus (P) is an essential macronutrient for plant growth and development that plays key roles in many processes, including energy metabolism and synthesis of nucleic acids and membranes (Raghothama, 1999). It is second only to nitrogen as the most limiting nutrient for plant growth (Bieleski, 1973; Raghothama, 1999;. In many soils, low availability of P is a limiting factor in crop production . Due to the low availability of soluble P in many ecosystems, plants have developed adaptive mechanisms that aid in the acquisition of P from soil. Strategies that lead to better uptake or acquisition include expanded root surface area through increased root growth and root hair development (Lynch and Brown, 1998;Gilroy and Jones, 2000; Williamson et al., 2001), organic acid synthesis and exudation (Dinkelaker et al., 1989;Johnson et al., 1996a;Jones, 1998; Aono et al., 2001;Massonneau et al., 2001; Sas et al., 2001), exudation of acid phosphatases (Duff et al., 1991; del Pozo et al., 1999;Gilbert et al., 1999;Miller et al., 2001), enhanced expression of phosphate transporters (Leggewie et al., 1997;Liu et al., 1998aLiu et al., , 1998b Chiou et al., 2001;Liu et al., 2001), and mycorrhizal associations (Marschner and Dell, 1994; Smith et al., 1994). Strategies aimed at conserving P involve internal remobilization of P and use of alternative metabolic pathways (Theodorou et al., 1992; Theodorou and Plaxton, 1993;Plaxton and Carswell, 1999).White lupin (Lupinus albus), a species known for its extreme tolerance for low P availability, has proven an illuminating model system for understanding plant adaptations to low P, despite its lack of mycorrhizal symbiosis. Instead, its adaptation to P deficiency (ϪP) is a highly coordinated modification of root development and biochemistry resulting in proteoid (or cluster) roots-short, densely clustered tertiary roots-that resemble bottlebrushes (Gardner et al., 1982(Gardner et al., , 1983Dinkelaker et al., 1995;Johnson et al., 1996b;Neumann et al., 1999;Massonneau et al., 2001). Unlike typical...

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White lupin (Lupinus albus) is a legume that is very efficient in accessing unavailable phosphorus (Pi). It develops short, densely clustered tertiary lateral roots (cluster/proteoid roots) in response to Pi limitation. In this report, we characterize two glycerophosphodiester phosphodiesterase (GPX-PDE) genes (GPX-PDE1 and GPX-PDE2) from white lupin and propose a role for these two GPX-PDEs in root hair growth and development and in a Pi stress-induced phospholipid degradation pathway in cluster roots. Both GPX-PDE1 and GPX-PDE2 are highly expressed in Pi-deficient cluster roots, particularly in root hairs, epidermal cells, and vascular bundles. Expression of both genes is a function of both Pi availability and photosynthate. GPX-PDE1 Pi deficiency-induced expression is attenuated as photosynthate is deprived, while that of GPX-PDE2 is strikingly enhanced. Yeast complementation assays and in vitro enzyme assays revealed that GPX-PDE1 shows catalytic activity with glycerophosphocholine while GPX-PDE2 shows highest activity with glycerophosphoinositol. Cell-free protein extracts from Pi-deficient cluster roots display GPX-PDE enzyme activity for both glycerophosphocholine and glycerophosphoinositol. Knockdown of expression of GPX-PDE through RNA interference resulted in impaired root hair development and density. We propose that white lupin GPX-PDE1 and GPX-PDE2 are involved in the acclimation to Pi limitation by enhancing glycerophosphodiester degradation and mediating root hair development.