Aijaz A. Wani

Aquaporins as potential drought tolerance inducing proteins: Towards instigating stress tolerance

Aquaporins (AQPs) are primarily involved in maintaining cellular water homeostasis. Their role in diverse physiological processes has fascinated plant scientists for more than a decade, particularly concerning abiotic stresses. Increasing examples of evidence in various crop plants indicate that the AQPs are responsible for precise regulation of water movement and consequently play a crucial role in the drought stress tolerance. Since drought is one of the major abiotic stresses affecting agricultural production worldwide, it has become a critical agenda to focus research on the development of drought tolerant crop plants. AQPs can act as key candidate molecules to confront this issue. Hence, there is an important need to explore the potential of AQPs by understanding the molecular mechanisms and pathways through which they induce drought tolerance. Moreover, the signalling network/s involved in such pathways needs to be mined and understood correctly, and that may lead to the development of drought tolerance in crop plants. In the present review, opportunity and challenges regarding the efficient utilization of AQP-related information is presented and discussed. The complied information and the discussion will be helpful for designing future experiments and to set the specific goals for the enhancement of drought tolerance in crop plants. Biological Significance Knowledge on the role of AQPs in maintaining cellular water homeostasis has given new hope for developing drought tolerance in crop plants. Since drought is one of the major abiotic stresses affecting agricultural production worldwide, it has become a critical agenda to focus research on the development of drought-tolerant crop plants. AQPs can act as key candidate molecules to solve this problem through genetic engineering. For this, it is important to understand the molecular mechanisms and inter-related pathways through which AQPs induce drought tolerance and to explore the signaling network/s involved in such pathways.

On correct identification, range expansion and management implications of Myriophyllum aquaticum in Kashmir Himalaya, India

The misidentification of Myriophyllum aquaticum (Vell.) Verdc. in the Kashmir Himalaya, India is corrected. In addition to its taxonomic description and illustration, the paper discusses the range expansion of this invasive plant species into different aquatic habitats and management implications in the region.

Mutagenic Effects on Meiosis in Legumes and a Practical Case Study of Vicia faba L.

Mutagens typically physical (ionising radiations, e.g. particulate (α-ray, β-ray and thermal neutrons) and non-particulate (X-ray and ɣ ray); non-ionising radiation, e.g. UV ray) and chemical (EMS, dES, NMG, MMS, EO, hydroxyl amine, nitrous acid, 5-bromouracil, 2-aminopurine and ethidium bromide, among others) are widely used in plant species of interest with an objective to create genetic variations by widening the gene pool and to induce gene mutation of commercial importance (superior qualitative trait(s) and enhancement in raw and value-added product(s)). Gene mutation is of global significance, and successful mutagenesis experiment depends on the sensitivity of the genotype(s) to the administered doses of the mutagen(s) employed. Assessment of LD50, lethality, injury, mitotic and meiotic aberration frequency (key components to determine sensitivity of a species) is prerequisite for determining sublethal doses for monitoring successful mutation breeding experiments. The chapter gives a comparative observation of ethyl methane sulphonate (EMS), methyl methane sulphonate (MMS) and gamma irradiation on cytological and developmental parameters, i.e. meiotic features, pollen sterility, seed germination and seedling survival in Vicia faba L. The present study on the Vicia faba L. var. minor and major in M1 generation showed that all the mutagens used elicit numerous chromosomal aberrations in meiosis and decrease in seed germination, pollen fertility and seedling survival. The combined treatments induced more chromosomal aberrations than the individual doses of mutagens which represents that combined treatments could be more effective in creating more favourable variability than individual doses in both the varieties, i.e. minor and major of Vicia faba L.

Genetics of resistance in apple against Venturia inaequalis (Wint.) Cke

Apple (Malus × domestica) is the third important fruit in terms of production and consumption worldwide. Apple scab caused by Venturia inaequalis is the most devastating disease of apple. In the apple-growing regions, many fungicides are sprayed to control the disease leading to increase in the production cost. Development of scab-resistant cultivars is the long-lasting solution to control the disease. In apples, more than 20 major scab resistance genes have been identified in various cultivars and few wild relatives. Of all these genes, Rvi6 derived from Malus floribunda has been most extensively used in different breeding programs. Gene for gene interactions of these resistance genes with the avirulence genes from V. inaequalis have been understood in many cases. QTL-based polygenic resistance has also been characterized in apple. Nucleotide Binding Site Leucine-Rich Repeats (NBS-LRR) have been identified from the apple genome and many of them have been characterized from the scab resistance region. Molecular markers associated with most of the major scab resistance genes have been identified and their position has been mapped on different linkage groups. Marker-assisted selection (MAS) can be helpful in speeding up and accurately identifying the scab-resistant parents and progeny. Pyramiding of several major resistance genes can be undertaken for more durable resistance against apple scab. The present paper reviews the Malus-Venturia pathosystem, current status of knowledge about scab resistance genes, and their application in breeding against apple scab.

A performance appraisal of size dependent reproduction and reproductive allocation: A case study of two Inula species from Kashmir Himalaya

In this study we investigated the size-dependent reproductive pattern of Inula racemosa and I. royleana (Asteraceae) growing at different reaches in the environs of the Kashmir Himalaya. Size effects on reproductive pattern were evaluated by determining the size-dependency of flowering probability and reproductive effort. The results showed that the probability of flowering increased significantly with the size of the plant in all populations, indicating that individuals do not flower until they reach a threshold size and considerable between-site differences were found in the slope and the intercept of the regression between plant size and flower production. In I. racemosa, populations at high altitudes had significantly lower threshold sizes for reproduction and showed sharp increase in flowering probability with plant size, compared to other populations at lower altitudes. However, no pattern in size-dependent flower production was found relative to the altitude in I. royleana, as flower production at some sites, at high altitudes, increased more steeply with plant size than at other sites. For both taxa, reproductive effort decreased allometrically as adults grew, as can be interpreted from the allometric relationship between reproductive and vegetative biomass. Further studies are required to determine whether population differentiation in size-dependent reproductive pattern is maintained by selection.

Asynapsis and Desynapsis in Plants

The pairing of chromosomes also known as synapsis is essential for facilitating crossing over and recombination of genes during prophase-I and segregation of homologous chromosomes during anaphase-I of meiosis. Mutations in genes controlling synapsis affect normal pairing of homologues during prophase-I are give rise to synaptic mutants. The first synaptic mutants were discovered in maize and since then have been reported in large number of plant species. These synaptic mutants show complete or partial lack of chromosome pairing during meiosis. Asynapsis is the complete failure of homologous chromosomes to pair or synapse during the first meiotic division, whereas, desynapsis is a condition where homologous chromosomes pair or synapse normally at the beginning of prophase, but later fail to maintain this association in the subsequent stages of meiosis and thus separate prematurely. Both asynapsis and desynapsis have been found to play significant role in origin of popyploids via formation of 2n gametes. The meiotic disturbance due to asynapsis and desynapsis also leads to the formation of various types of aneuploids..

Polyploidy: Evolution and Crop Improvement

The condition of possessing more than two complete genomes in a cell has intrigued biologists almost a century. Many plant species including flowering plants are polyploids, and we know that it has a significant role in the evolution and crop improvement. It is well tolerated in many groups of eukaryotes. Polyploid ancestors have given rise to a number of flowering plants. Despite its widespread occurrence, the direct effect of polyploidy on evolutionary success of a species is still largely unknown. Many attractive hypotheses have been proposed in order to assign functionality to the increased content of a duplicated genome. Among these hypotheses are the proposals that genome doubling confers various advantages to polyploids which allow them to thrive well in environments that pose challenges to their diploid progenitors. Polyploidy is often accompanied with formation of improved varieties, developing sterile lines, restoring fertility in hybrids, enlargement and enhanced vigor, increasing allelic diversity and heterozygosity, etc. In genome-wide context for optimizing marker-assisted selection and crop plant improvement, all these factors need to be considered. This chapter attempts to give a brief overview of polyploidy, its origin, and role in evolution and crop improvement.

Laboratory Techniques of Studying Plant Chromosomes

Study of chromosomes helps in revealing the basic number, structure, and behavior of chromosome complement of a particular species which can then be compared with that of another species. The properties of chromosomes remain constant within a particular species and change only upon hybridization and/or evolution. As such, by studying the chromosomes, the parental lineage or evolutionary history can be elucidated. Also, we can find a relation between the chromosome complement and the phenotype of the species. On the basis of the properties of the chromosome complement, various taxonomic rearrangements have been made. Several of the plant species are polyploid, having a multiple set of basic chromosomes. The sterility and fertility of a species can be ascertained to the odd or even number of chromosome complement, respectively. The biggest challenge in chromosomal study is to obtain deeply stained, condensed chromosomes with well-defined primary and secondary constrictions. For this, every step is optimized according to the type of tissue and the type of species being studied. For this a variety of metallic and nonmetallic chemicals have been used in combination for fixation with varied time durations accompanied with different types of stains. Sometimes the use of mordants becomes necessary in order to enhance the staining properties. The traditional method of chromosome study by sectioning has largely become outdated and replaced by fast, easy, and low-cost squash and smear techniques. The meiotic chromosomes are studied through anther smear, whereas the somatic chromosomes are commonly studied through root tip squashing. Lately, chromosomal banding techniques have proved to be an additional tool in the hands of cytogeneticists for detailed chromosomal studies. In this chapter an attempt has been made to revisit the available procedures for studying plant chromosomes through squash and smear techniques and the fixatives and stains used therein in light of the available literature.

Banding Techniques in Chromosome Analysis

Chromosome identification has been traditionally based on morphological features of individual chromosomes such as chromosome length, arm ratio and primary and secondary constriction collectively called as karyotype. A number of stains such as acetocarmine, Feulgen and aceto-orcein all of them being whole chromosome stains have been used in these studies. Although classical staining helps in studying chromosome morphology, structural and numerical variations, however, morphologically similar chromosomes cannot be distinguished. The utilization of fluorescent and other dyes together with various modifications in pretreatment of cytological material in the late 1960s led to the discovery of various banding techniques which proved to be additional tool for identification of individual chromosomes. New and reliable staining procedures were introduced; each was capable of revealing a unique banding pattern of the chromosomes of a given species. The advantage with banding techniques is that they can resolve morphologically similar as well as different chromosomes and help in understanding the chromosome organization. Chromosome banding is a lengthwise variation in staining properties along a chromosome based on the GC- or AT-rich regions or constitutive heterochromatin. A single dye or fluorochrome can often be used to produce a banding pattern on a chromosome. A band is a part of chromosome which is clearly distinguishable from its adjacent segment by appearing darker or lighter with various banding methods. The Paris Conference – 1971 – classified banding techniques as Q–banding (fluorescence based), C–banding (constitutive heterochromatin (AT- or GC-rich DNA)), G–banding (whole length banding (Giemsa staining)), R–banding (reverse of G–banding) and Ag-NOR stain (nucleolar organizing regions). All these banding techniques have led to a more precise cytogenetic and phylogenetic analysis of various eukaryotes. The major applications of banding techniques have been the mapping of genes on chromosomes and identification of chromosome alterations such as deletions, duplications, translocations and aneuploidy. They have also played an important role in measuring the amount of heterochromatin among individuals.

Cytomixis: Causes and Consequences as a Case Study in Vicia faba L.

Broad bean (Vicia faba L.) is a member of the family Fabaceae which showed cytomixis during microsporogenesis. Cytomixis is proposed to be caused by genes, abnormal cell wall formation, action of chemicals, changes in the biochemical process, imbalanced and sterile genetic systems, persistence of male-sterile mutant genes, and frequent alterations in environmental factors. The cytomixis was found to happen through different methods, i.e., cytoplasmic channels and direct fusion method in the meiocytes. The former was more abundant than the latter, and both the methods were found in various phases of microsporogenesis. The transfer of chromatin material involved the whole diploid set of chromosomes or some chromosomes in the diploid set from donor to recipient cell/cells. The PMCs which showed deviation from the basic diploid chromosome number by cytomixis may lead to the formation of aneuploid and polyploid gametes. Stickiness was found in all the mutagen-treated population and showed dose-dependent increase with the mutagens. There was found positive correlation between the pollen fertility, cytomixis, and chromosomal stickiness. Genetic factors might have been also contributed toward decrease in pollen fertility. The cytomixis was reported in both the varieties of Vicia faba L., but the var. minor showed more frequency than var. major along with stickiness and reduction in pollen fertility indicating its greater sensitivity to the mutagens.