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DNA amplification fingerprinting (DAF) was used to evaluate the genetic relationships among 11 cultivars of poinsettia (Euphorbia pulcherrima Willd.). Amplification was with 10 octamer oligonucleotide primers that generated 336 DNA bands. Thirty-one percent of the bands were polymorphic and distinguished among cultivars. Genetic relationships were evaluated by cluster analysis, and the resulting dendrogram closely agreed with published cultivar relationships. Arbitrary signatures from amplification profiles (ASAP) were further used to characterize two cultivars, `Nutcracker Red' and `Peterstar Red', that were previously found to be genetically and morphologically similar, as well as five cultivars in the “Freedom” series. The DAF products generated with arbitrary octamer primers were reamplified with mini-hairpin decamer primers in these experiments. The ASAP profiles were complex and yielded a total of 231 bands, 38% of which were polymorphic and capable of distinguishing each Freedom cultivar. Five of the eight primer combinations distinguished `Nutcracker Red' from `Peterstar Red'. Thus, closely related cultivars of poinsettia can be separated using new and improved molecular fingerprinting protocols.
Our objectives were to determine (a) if mycorrhizal (VAM) fungi can alter drought-induced, nonhydraulic regulation of shoot growth, and (b) how much of a root system can be dried or severed before hydraulic effects on shoot responses become evident. Sorghum was grown with roots equally divided among four pots. The 2×2×4 factorial design had two levels of mycorrhizae (± Glomus intraradix), two levels of root treatment (dried or severed) and four levels of amount of roots treated (0, 1, 2 or 3 pots dried or severed). Neither leaf water potential (Ψ) nor Cs were affected by drying 1 or 2 pots, and reductions in leaf area in these plants were therefore attributed to nonhydraulic signalling. When 2 pots were dried, leaf growth was reduced less in VAM than in nonVAM plants, despite lower P in VAM leaves and despite quicker soil drying by VAM roots. Drying or severing roots of 3 pots did result in drops in leaf Ψ and Cs, indicating a likely hydraulic effect on leaf water status in those plants. Leaf P declined progressively as more roots were dried or severed, possibly also affecting growth in plants with roots in 3 pots dried or severed. Leaf extension rates (LER) declined with only slight drops in soil Ψ, and LER declines were related to volume of soil drying. In VAM plants, leaf area reductions were correlated with length of time roots were exposed to soil Ψ between -0.02 and -0.50 MPa.
In Zea mays L. plants grown with roots divided between two pots, we tested (a) if leaf P concentration can affect nonhydraulic root to shoot signalling of soil drying, and (b) if a mycorrhizal (VAM) effect on signalling can occur independently of a VAM effect on leaf P. The 2×3×2 factorial design had 2 levels of mycorrhizae (± Glomus intraradix Schenck & Smith), 3 levels of P fertilization and 2 levels of water (both pots watered, or one pot watered while the other was allowed to dry). Total leaf length and shoot dry weight were not reduced in half-dried VAM plants, but each measure was ultimately reduced about 10% in half-dried nonVAM plants. Stomatal conductance (Cs), unaffected by VAM, was lower in half-dried, high-P plants than in high-P controls a few times during the latter half of the experiment, by as much as 65%. Leaf water potentials were not affected by partial soil drying, and reductions in leaf growth preceded reductions in Cs; hence, growth reductions were attributed to nonhydraulic signals coming from roots in drying pots. VAM × water and P × water interactions indicated that mycorrhizae influenced signal effects on final plant leaf length and that P fertilization influenced signal effects on Cs. Soil water potential, measured every 2 h with heat dissipation sensors, showed that soil drying was not affectd by VAM or P treatment.
We compared the potential for foliar dehydration tolerance and maximum capacity for osmotic adjustment in twelve temperate, deciduous tree species, under standardized soil and atmospheric conditions. Dehydration tolerance was operationally defined as lethal leaf water potential (Ψ): the Ψ of the last remaining leaves surviving a continuous, lethal soil drying episode. Nyssa sylvatica and Liriodendron tulipifera were most sensitive to dehydration, having lethal leaf Ψ of –2.04 and –2.38 MPa, respectively. Chionanthus virginiana, Quercus prinus, Acer saccharum, and Quercus acutissima withstood the most dehydration, with leaves not dying until leaf psi dropped to –5.63 MPa or below. Lethal leaf Ψ (in MPa) of other, intermediate species were: Quercus rubra (–3.34), Oxydendrum arboreum (–3.98), Halesia carolina (–4.11), Acer rubrum (–4.43), Quercus alba (–4.60), and Cornus florida (–4.88). Decreasing lethal leaf Ψ was significantly correlated with increasing capacity for osmotic adjustment. Chionanthus virginiana and Q. acutissima showed the most osmotic adjustment during the lethal soil drying episode, with osmotic potential at full turgor declining by 1.73 and 1.44 MPa, respectively. Other species having declines in osmotic potential at full turgor exceeding 0.50 MPa were Q. prinus (0.89), A. saccharum (0.71), Q. alba (0.68), H. carolina (0.67), Q. rubra (0.60), and C. florida (0.52). Lethal leaf Ψ was loosely correlated with lethal soil water contents and not correlated with lethal leaf relative water content.