Ioan Has

Density effects on environmental variance and expected response to selection in maize (Zea mays L.)

The study aimed to address the optimal plant population density in maize that maximizes phenotypic expression and differentiation, and lessens environmental effects on genotypic expression in terms of the response to selection. A set of seven short-season hybrids (Rom set) was tested under rainfed conditions (2006, 2007) in Romania, and a set of seven long-season hybrids (Gr set) was tested with irrigation (2007) in Greece. Experimentation was conducted under ultra-low (ULD), low (LD), middle (MD), and high (HD) densities (0.74, 2.51, 4.20, 8.40 plants/m2 for the Rom set, and 0.74, 3.13, 6.25, 8.33 plants/m2 for the Gr set). Phenotypic expression and differentiation for grain yield were highest at the ULD. Coefficient of variation (CV) for grain yield, ear length and kernel row number decreased as density decreased. Environmental conditions and hybrid plant-yield potential (i.e., maximum yield per plant) were crucial for the optimal density that achieved the lowest environmental variance. For the Rom set the lowest CV for grain yield was obtained at the LD in the unfavourable season and at the ULD in the favourable season. The less acquired variance was achieved at the ULD for the highest yielding hybrids and at the LD for the lowest yielding hybrids, revealing a negative association between plant-yield potential and optimal density. Concluding, a density proximal to the ULD approximates absence of competition in maize, and optimizes three determinant parameters for successful selection: selection intensity, heritability and phenotypic differentiation.

Maize Cytolines Unmask Key Nuclear Genes That Are under the Control of Retrograde Signaling Pathways in Plants

The genomes of the two plant organelles encode for a relatively small number of proteins. Thus, nuclear genes encode the vast majority of their proteome. Organelle-to-nucleus communication takes place through retrograde signaling (RS) pathways. Signals relayed through RS pathways have an impact on nuclear gene expression but their target-genes remain elusive in a normal state of the cell (considering that only mutants and stress have been used so far). Here, we use maize cytolines as an alternative. The nucleus of a donor line was transferred into two other cytoplasmic environments through at least nine back-crosses, in a time-span of > 10 years. The transcriptomes of the resulting cytolines were sequenced and compared. There are 96 differentially regulated nuclear genes in two cytoplasm-donor lines when compared with their nucleus-donor. They are expressed throughout plant development, in various tissues and organs. One-third of the 96 proteins have a human homolog, stressing their potential role in mitochondrial RS. We also identified syntenic orthologous genes in four other grasses and homologous genes in Arabidopsis thaliana. These findings contribute to the paradigm we use to describe the RS in plants. The 96 nuclear genes identified here are not differentially regulated as a result of mutation, or any kind of stress. They are rather key players of the organelle-to-nucleus communication in a normal state of the cell.

The role of cytoplasmatic diversification on some productivity traits of maize

The discovery of cytoplasmic male sterility directed scientists to focus their research on the role and influence of cytoplasmic factors on the heredity of some important agronomic traits, especially in hybrids. In this context, numerous cytolines have been created at the Agricultural Research and Development Station Turda (Romania) in order to assess if their genetic value could be due to cytoplasm diversification. Backcross was performed for ten generations in order to transfer the nucleus of the pollenator into the cytoplasm of the maternal genotype. This paper presents the results regarding yield and yield components of 100 hybrids, originated from crosses among isolines and four testers. The isolines, used as maternal genotypes, were created by transferring the nucleus of the elite inbred lines TC 209, TC 316, TC 243, TB 367 and D 105 onto the cytoplasm of T 248, TB 329, TC 177 and TC 221 inbred lines. The cytoplasms–nucleus interaction and the triple cytoplasm–nucleus–tester interaction, caused significant differentiation between the hybrids originated from cytoline maternal genotype in comparison to those from original inbred lines. Yield, thousand kernel weight, ear weight, grain weight/ear and the number of kernels/row were used for comparisons among all genotypes used into this research.

Determination of Amino Acids in Corn Seed by Gas Chromatography–Mass Spectrometry

A gas chromatography–mass spectrometry method was developed for the determination of free amino acids from corn inbred lines flour. Amino acids were extracted using 6% trichloroacetic acid. The extracts were purified using an ion-exchange solid phase, derivatized as trifluoroacetic butyl esters, and analyzed. The 15N-methionine was used as the internal standard. The method was repeatable for most of the amino acids (coefficient of variation was in the order of 20%), and good accuracy and limits of detection were obtained. Among the free amino acids determined, the highest concentrations were obtained for aspartic acid, proline, gamma-aminobutyric acid, lysine, alanine, glutamic acid, and histidine. The study established the variation of the free amino acids within the inbred lines.