SummaryRoot hairs are a major site for the uptake of water and nutrients into plants, and they form an increasingly important model system for the study of development in higher plants. We now report on the molecular genetic analysis of the srh1 mutant in Arabidopsis thaliana impaired in root hair tip growth. We show that srh1 is a new allele of cow1 (can of worms1) and we identified the COW1 gene using a positional cloning strategy. The N-terminus of the COW1 protein is 32% identical to an essential phosphatidylinositol transfer protein (PITP), the yeast Sec14 protein (sec14p) while the C-terminus is 34.5% identical to a late nodulin of Lotus japonicus, Nlj16. We show that expression of the COW1 lipid-binding domain complements the growth defect associated with Sec14p dysfunction in yeast. In addition, we show that GFP fused to the COW1 protein specifically accumulates at the site of root hair outgrowth. We conclude that the COW1 protein is a PITP, essential for proper root hair growth.

The prasinophycean alga Mantoniella squamata uses in vivo an incomplete violaxanthin cycle. Although the violaxanthin cycle in Mantoniella is capable of converting violaxanthin to zeaxanthin, in intact cells only antheraxanthin accumulates during periods of strong illumination. Antheraxanthin enhances non-photochemical quenching of chlorophyll¯uores-cence. Inhibition of antheraxanthin synthesis by the deepoxidase inhibitor dithiothreitol abolishes increased thermal energy dissipation. Antheraxanthin-dependent non-photochemical quenching, like zeaxanthin-mediated non-photochemical quenching in higher plants, is uncoupler-sensitive. Mantoniella squamata cells cultivated at high light intensities contain higher amounts of violaxanthin than cells grown at low light. The increased violaxanthin-cycle pool size in high-light-grown Mantoniella cells is accompanied by higher de-epoxidation rates in the light and by a greater capacity to quench chlorophyll¯uorescence non-photochemically. Antheraxanthin-dependent ampli®cation of non-photochemical quenching is discussed in the light of recent models developed for zeaxanthin-and diatoxanthin-mediated enhanced heat dissipation.Key words: Antheraxanthin ± Light adaptation ± Mantoniella ± Non-photochemical quenching of chlorophyll¯uorescence ± Violaxanthin cycle ± Zeaxanthin Abbreviations and symbols: Chl chlorophyll; Fm H ¯uores-cence yield under conditions of membrane energization or recovering¯uorescence after actinic illumination; Fm maximum uorescence level with PSII reaction centers closed;Fo minimum¯uorescence with open PSII reaction centers; LHC light-harvesting complex; LHCII light-harvesting complex of PSII; NPQ non-photochemical quenching; PFD photon¯ux density Correspondence to: C.

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We have studied carotenoid biosynthesis in the prasinophycean alga Mantoniella squamata, which contains a great variety of carotenoids belonging to both the alpha- and the beta-carotene (Car) biosyntheses pathways. This unusual carotenoid composition allowed us to address the problem of how biosynthesis on the alpha- and the beta-Car pathway is regulated in response to different light regimes. We found that illumination with 4 h of actinic high light (HL, 250 micromol m(-2) s(-1)), and culture growth in permanent light (PL, 60 micromol m(-2) s(-1)). induced the de novo synthesis of violaxanthin (Vx) cycle pigments belonging to the beta-Car pathway. Carotenoid synthesis on the alpha-Car biosynthesis pathway led to a strong accumulation of lutein (L) and dihydrolutein (DhL). Both the newly synthesised Vx cycle pigments and L/DhL can be regarded as intermediate pools of carotenoids that were converted to light-harvesting pigments in low light (LL) periods following the phases of HL illumination. This transition to the light-harvesting pigments included the conversion of Vx to neoxanthin (Nx) on the beta-Car pathway, and the transformation of L/DhL to prasinoxanthin (Px), the main light-harvesting pigment of M. squamata belonging to the alpha-carotenoids. Isolation of light-harvesting complexes from L-enriched M. squamata cells showed that both L and the Vx cycle pigments were loosely bound to the LHC apoprotein. This peripheral binding is in agreement with their proposed role as intermediate pigments in the biosynthesis of light-harvesting pigments, and should allow a smooth detachment from the protein in periods of LL when the synthesis of Nx and Px is stimulated. We conclude that carotenoid synthesis proceeds in general in an economical way: in both, the alpha- and the beta-Car pathway HL induces the formation of photoprotective pigments, which in LL periods following the HL illumination are not degraded, but on the contrary are converted to light-harvesting pigments.

Blakeslea trispora (Mucorales) has economic importance because of its ability to produce large amounts of beta-carotene. To shed light on the actual point of induction and to shorten the following production process, germination and growth of its two mating types, (-) and (+), were observed separately, and the mating point was investigated in lab scale experiments. The (-) mating type showed much faster germination than the (+) type on solid medium and in Erlenmeyer flasks. However, after a first period, the (-) mating type grew clearly slower than the (+) type. In addition, the (-) type branched more vividly than the (+) type. A ratio of 30:1 of (-) and (+) type at an age of 20 h was found to achieve highest beta-carotene yields. Our results provide a comprehensive overview of Blakeslea trispora growth and its product synthesis.