THE MAIZE VP*404 MUTANT IS IMPAIRED IN MOCO-S BIOSYNTHESIS.

part 1: DESICCATION TOLERANCE In maize, desiccation tolerance is acquired by the embryo at a precise developmental stage, between 20 and 25 DAP (days after pollination) and is probably related to the maturation process characterized by the accumulation of storage products and LEA (late embryogenesis abundant) proteins, that have a protective role. In viviparous (vp) mutants, that are deficient in ABA synthesis or lack an active vp1 factor, embryos do not express the normal set of maturation phase proteins; it is also conceivable that these embryos do not acquire the desiccation tolerance. To verify this, we applied premature desiccation to developing vp embryos about 25 DAP, and compared their germination capacity to embryos not subjected to such treatment. When cultured immediately after their excision, immature embryos of all mutants tested germinated with a high frequency (95-100%) similarly to their wild type counterparts. if they were cultured following a premature dehydration treatment, only vp1 and vp10 maintained a partial desiccation tolerance while the other mutants lost it. These results seem to suggest that acquisition of desiccation tolerance requires the completion of the steps between carotenoid production and the later stages of ABA biosynthesis, with a possible protective role of carotenoid against oxidative phenomena that take place even during desiccation, because the metabolism is still active. part 2: THE MAIZE vp*404 MUTANT is IMPAIRED in Moco BIOSYNTHESIS In maize the vp10 and vp15 genes have been isolated; they encode the orthologs of the Arabidopsis Cnx1, and Cnx7 respectively, which catalyse the last steps of Moco-O biosynthesis. Moco-O is required for the activity of both Nitrate Reductase and Sulfite Oxidase. Maize mutants defective in Moco-S are instead unknown, but Moco-S mutant plants have been described for Arabidopsis (ABA3), tomato (flacca) and tobacco (ABA1), which lack AO and XDH activities, but show normal NR enzymatic activity. These mutants show a wilty phenotype and are impaired in stress responses. vp*404 is a viviparous mutant with light green seedlings, reduced content of chlorophyll, carotenoids and ABA.Complementation tests with all viviparous mutants with green seedlings reported in literature showed that vp*404 defines a new vp gene. Moco enzyme activities analysis showed normal value for SO and an extremely reduced activity for both AO and XDH, suggesting that vp*404 is likely a Moco-Sulfurase defective mutant. In Arabidopsis the ABA3 gene encodes the Moco-Sulfurase. Blast analysis performed with the ABA3 sequence , gave two sequences with high Identity on chromosome 6. The two sequences, which are 30kb distal, encode the Moco-S N-terminal and the Moco-S C terminal domain respectively. However,since in all Eukaryotes analysed the two protein domains are encoded by the same gene, we refer to the gene in Sorghum as a model, and we have reconstructed in silico the structure of a maize unique theoretical gene, in which the C terminal domain was correctly oriented and 30,000bp between the two domains were arranged. Specific primers were designed on the basis of the theoretical gene and the corresponding cDNA sequence was analysed by means of a RT-PCR approach. Preliminary data seem to confirm the proposed gene model, however gene isolation and sequence analysis will be necessary to confirm our hypothesis

Azolla-Anabaena as a Biofertilizer for rice paddy fields in the Po Valley, a temperate rice area in Northern Italy

Azolla is a floating pteridophyte, which contains as endosymbiont the nitrogen-fixing cyanobacterium Anabaena azollae (Nostocaceae family). Widely cultivated in the Asian regions, Azolla is either incorporated into the soil before rice transplanting or grown as a dual crop along with rice. To examine the feasibility of its use in flooded rice fields sited in the Temperate European Areas, we carried out a series of experiments in PVC tanks during 2000–2002 in Po Valley (northern Italy) conditions, to study the growth-development dynamics and the resistance/tolerance to low temperatures and to commonly used herbicides of several different Azolla strains. Three out of five strains tested survived the winter, with an increase in biomass from March to May producing approximately 30–40 kg ha−1 of nitrogen. One of these strains, named “Milan”, emerged as the most resistant to herbicide and the most productive. Of the herbicides tested, Propanil permitted the survival of growing Azolla

Microscale material variability and its effect on longitudinal tensile failure of unidirectional carbon fibre composites

This paper deals with modelling the effect of local fibre volume fraction variability, fibre misalignment and fibre strength variability on the longitudinal tensile strength of unidirectional plies with finite element analysis. Variability is accounted for by generating spatially-correlated fields of fibre misalignment and volume fraction. This information is then translated into local mechanical properties and orientations in finite element models of the ply, which are virtually tested in longitudinal tension. Monte Carlo simulations were performed to evaluate the effect of different sources of material variability, i.e. local fibre strength, fibre volume fraction and misalignment. Ply strength predictions lowered when including the variability of local volume fraction and fibre misalignment in the modelling, showing a better agreement with experiments for the carbon/epoxy system investigated

Micro-mechanical modelling of longitudinal compression in unidirectional composites: effect of misalignment

Unidirectional composites exhibit their best performances when loaded in the longitudinal direction, exploiting the high stiffness and strength of the reinforcements. In longitudinal compression, the strength is significantly lower if compared to tension. This is due to the inherent material imperfections, such as fibre misalignment, that trigger the formation of kink bands and micro-buckling of fibres under compression. The phenomena involved in longitudinal compression are very complex. According to some authors, failure is governed by the matrix yielding and the fibre-matrix debonding, promoted by fibre misalignment. Predictive models in the literature consider these phenomena to capture the kink band formation. In this work, a micromechanical model based on finite elements is used to simulate the longitudinal compressive behaviour of a unidirectional composite. The microstructure is generated based on an algorithm, extended to include misalignment. The features of the model are: i) fibre-matrix interfaces modelled with cohesive elements, ii) matrix plasticity and damage, to account for the non-linear behaviour of the matrix; iii) sinusoidal misalignment and iv) random geometrical arrangement in the transverse direction. The results of this investigation are compared with other similar works in the literature, both with finite element and analytical formulations. The results of this work are the first part of a broader research, aimed to investigate more realistic 3D misalignments and its effect on compressive strength

Interaction between different genes controlling endosperm development in maize

In this report we present the results of a complementation test involving nine emp (empty pericarp) mutants of maize that represent single gene mutants, isolated as independent events. These mutants are embryo lethal at maturity and drastically reduced in their endosperm size. They can be subdivided in two major subgroups: those with a flat appearance of the kernel and those with a wrinkled pericarp. By crossing inter-se plants heterozygous for emp mutants, we identified those non-complementing (that means allelic) and those complementing (that means not allelic) in the F1 generation. Most results in the F1 were concordant to those obtained in the F2 generation with the exception of four cases where the F1 results suggest allelism (i.e. one gene) whereas those in the F2 segregation of two genes. This intriguing result seems to suggest an interaction between different emp mutants due to second site non-complementation (SSNC). In addition while scoring ears segregating for a single emp mutant, in different genetic backgrounds, we noticed that some mutant seeds exhibited a more abundant endosperm tissue and occasionally an embryonic axis. About 10% of these seeds germinate yielding slow growing seedlings. This observation could be explained by assuming that emp mutants introduced in different genetic backgrounds uncover a cryptic variability. This point needs to be further investigated but if confirmed, emp mutants could be used as a tool for the detection of genetic factors contributing to the amount of endosperm in the maize kernel to exploit in breeding programs

Vivipary as a tool to analyze late embryogenic events in maize

In maize vivipary, the precocious germination of the seed while still attached to the ear, is the diagnostic phenotype of mutants, which are impaired in the biosynthesis or response to abscisic acid (ABA). Of the 15 genes so far described, 12 control specific steps in ABA biosynthesis, two mediate hormone response and one still has an undefined role. We have analyzed a collection of 25 independent vp isolates with the aim of determining the degree of mutational saturation that has so far been reached. Of the 25 viviparous mutants complementation tested, 22 correspond to known loci: six are allelic to vp1, another six to vp5, one to vp7, two to vp9, six to vp10 and one to w3. The remaining three represent genes not previously identified. All mutants so far tested except rea show a decrease in ABA content. As to the only two mutants (vp1 and rea) whose endogenous ABA content is not impaired, the reduction in sensitivity of the double mutant compared to the single ones suggests that the two genes control separate pathways in the ABA signal transduction. Some of the mutants in this collection have a characteristic incomplete germination that allows the embryo of the mature dry seed to resume germination. By exploiting this feature it is possible to infer, through a germination test, whether the mutant has been impaired in the acquisition of desiccation tolerance. This information provides the starting point for the dissection of the genetic basis of desiccation tolerance