Root enhancement in cytokinin-deficient oilseed rape causes leaf mineral enrichment, increases the chlorophyll concentration under nutrient limitation and enhances the phytoremediation capacity

Background Cytokinin is a negative regulator of root growth, and a reduction of the cytokinin content or signalling causes the formation a larger root system in model plants, improves their growth under drought and nutrient limitation and causes increased accumulation of elements in the shoot. Roots are an important but understudied target of plant breeding. Here we have therefore explored whether root enhancement by lowering the cytokinin content can also be achieved in oilseed rape (Brassica napus L.) plants. Results Transgenic plants overexpressing the CKX2 gene of Arabidopsis thaliana encoding a cytokinin-degrading cytokinin oxidase/dehydrogenase showed higher CKX activity and a strongly reduced cytokinin content. Cytokinin deficiency led to the formation of a larger root system under different growth conditions, which was mainly due to an increased number of lateral and adventitious roots. In contrast, shoot growth was comparable to wild type, which caused an enhanced root-to-shoot ratio. Transgenic plants accumulated in their leaves higher concentrations of macro- and microelements including P, Ca, Mg, S, Zn, Cu, Mo and Mn. They formed more chlorophyll under Mg- and S-deficiency and accumulated a larger amount of Cd and Zn from contaminated medium and soil. Conclusions These findings demonstrate the usefulness of ectopic CKX gene expression to achieve root enhancement in oilseed rape and underpin the functional relevance of a larger root system. Furthermore, the lack of major developmental consequences on shoot growth in cytokinin-deficient oilseed rape indicates species-specific differences of CKX gene and/or cytokinin action

Histochemical localization of cytokinin oxidase/dehydrogenase during the developmental stages of Withania somnifera (L.) Dunal

Withania somnifera (L.) Dunal is a promising herb that has been used as both traditional and modern therapeutic agent by virtue of its bioactive compounds especially withanolides. Earlier in vitro studies revealed the relation between cytokinin (CK) level and biogeneration of withanolides. The information on the cytokinin metabolism in W. somnifera is lacking. The role of enzymes involved in cytokinin metabolism can provide the link between the level of cytokinin and withanolide production. CK is a plant growth regulator playing crucial role in almost all the developmental processes. It is agreed that, the oxidative breakdown of CK by cytokinin oxidase (CKX) is an important process by which plant tissues control the levels and distribution of CK. This paper reports histochemical localization of CKX at various developmental stages of W. somnifera.Key words: Cytokinin oxidase/dehydrogenase, Withania somnifera, CKX localization

The distribution of the first elementary divisor of the reductions of a generic Drinfeld module of arbitrary rank

Let $\psi$ be a generic Drinfeld module of rank $r \geq 2$. We study the first elementary divisor $d_{1, \wp}(\psi)$ of the reduction of $\psi$ modulo a prime $\wp$, as $\wp$ varies. In particular, we prove the existence of the density of the primes $\wp$ for which $d_{1, \wp} (\psi)$ is fixed. For $r = 2$, we also study the second elementary divisor (the exponent) of the reduction of $\psi$ modulo $\wp$ and prove that, on average, it has a large norm. Our work is motivated by the study of J.-P. Serre of an elliptic curve analogue of Artin's Primitive Root Conjecture, and, moreover, by refinements to Serre's study developed by the first author and M. R. Murty

The effects of magnetic field on the d-density wave order in the cuprates

We consider the effects of a perpendicular magnetic field on the d-density wave order and conclude that if the pseudogap phase in the cuprates is due to this order, then it is highly insensitive to the magnetic field in the underdoped regime, while its sensitivity increases as the gap vanishes in the overdoped regime. This appears to be consistent with the available experiments and can be tested further in neutron scattering experiments. We also investigate the nature of the de Haas- van Alphen effect in the ordered state and discuss the possibility of observing it.Comment: 5 pages, 4 eps figures, RevTex4. Corrected a silly but important typo in the abstrac