Growth and yield of wheat is enhanced when plants are provided with mixtures of NO3 and NH4, compared with either form alone. The objective of this experiment was to further evaluate the effects of N form on growth and tillering of wheat, with particular attention to tiller phenology, root morphology, and N uptake. Two species of spring wheat (Triticum durum Desf. cv. Inbar and Triticum aestivum L. cv. Len) were grown in the greenhouse with five different ratios of NO3‐N and NH4‐N (100/0, 75/25, 50/50, 25/75, 0/100). Compared with either form alone, mixtures of NO3 and NH4 increased vegetative growth of both cultivars due to enhanced development of coleoptilar and higherorder tillers. The magnitude of growth enhancement was greater (=60%) for Inbar than Len. For both cultivars, growth on N mixtures increased the number, mass, and primary branching of nodal roots, but did not affect seminal root growth. However, because nodal roots per tiller and nodal root branches per tiller were unaffected by N treatment or cultivar, changes in root morphology cannot fully explain treatment‐induced differences in tillering. Although plants of both cultivars supplied with mixed N absorbed more total N, the response was larger for Inbar because of its ability to sustain NO3 uptake when external NO3 concentrations were reduced by substitution with NH4, and to more than compensate for the decrease in NO3 uptake by additional absorption of NH4. Therefore, mixed‐N‐induced increases in tillering are also related to enhanced N uptake as well as altered root growth.
Supplying wheat plants with mixtures of NO~-and NH4 + increases growth and tiller production, but the physiological basis is unclear. Our objectives were to evaluate the roles for cytokinins and N use (e.g., accumulation, distribution, and utilization of absorbed N to produce tillers) in eliciting this response. Two species of spring wheat (Triticum aestivum L. cv. Len and Triticum durum Desf. cv. Inbar) were grown hydroponically in the greenhouse with N supplied as all NO~-, all NH4 + , or an equal mixture of each form. In one experiment, the synthetic cytokinin N6-benzylaminopurine (100 pM) was applied repeatedly (a total of five times) to the shoots during tiller initiation and development, while in another, xylem exudate was collected from cut stumps during the early stages of tiller development. Plants not sprayed with cytokinins produced more tillers and accumulated more N when grown with mixed N than with either N form alone. Cytokinin sprays did not affect tillering of mixed N plants but increased tillers in all-NOr-grown or alI-NH~+-grown plants to levels close to that obtained with mixed N. For unsprayed plants, the presence of NH~ increased the shoot/root ratio, the proportion of N in the shoot, and the efficiency with which absorbed N was used to produce tillers, compared with plants grown with all NOa-. Exogenous cytokinin appeared to mimic the effects of mixed N (and in some cases NH4 +) in altering the distribution and use of N by the plant. In addition, plants grown with mixed N or all NH4 + exhibited higher concentrations and mass transfer of cytokinins in the xylem than those supplied with all NO~-. These data are consistent with the interpretation that mixed N enhancement of tillering in wheat is due to increased synthesis of cytokinins, induced in part by use of NH4 +-N. F OR CEREAL CROPS such as wheat, the number of ears per plant is determined by the extent of lateral bud growth. This number depends on the species, the cultivar, the size and vigor of the seed, and various environmental factors such as light intensity, photoperiod, temperature, and availability of water and mineral nutrients during the period of tiller formation (Simons, 1982). Cytokinins are also known to be associated with the growth and development of tiller buds (
Abstract. Let p be a prime, and k be an algebraically closed field of characteristic p. In this paper, we provide the classification of connected Hopf algebras of dimension p 3 , except for the case when the primitive space of the Hopf algebra is a two-dimensional abelian restricted Lie algebra. Each isomorphism class is presented by generators x, y, z with relations and Hopf algebra structures. Let µ be the multiplicative group of (p 2 + p − 1)-th roots of unity. When the primitive space is one-dimensional and p is odd, there is an infinite family of isomorphism classes, which is naturally parameterized by A 1 k /µ.
Abstract. Let H be a finite-dimensional connected Hopf algebra over an algebraically closed field k of characteristic p > 0. We provide the algebra structure of the associated graded Hopf algebra grH. Then, we study the case when H is generated by a Hopf subalgebra K and another element and the case when H is cocommutative. When H is a restricted universal enveloping algebra, we give a specific basis for the second term of the Hochschild cohomology of the coalgebra H with coefficients in the trivial H-bicomodule k. Finally, we classify all connected Hopf algebras of dimension p 2 over k.
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