Consider the grasses

The identification of grasses relies heavily upon the structure ofspikelets, which, at first sight, appear to be very complicated. This article attempts to show that this complexity is more apparent than real. Spikelets display an enormous range in the shape and peculiar modifications of their separate parts, but all are constructed on the same basic plan. By relating the unfamiliar terminology for spikelet parts with that for more conventional inflorescences, and by showing how spikelets which look very different can be interpreted as variations on one basic theme, it is hoped that the initial difficulties experienced by many people when they attempt to name grasses will be largely overcome.     

Comparative genetics in the grasses

Comparative genetic studies have demonstrated that gene content and orders are highly conserved, both at the map and megabase level, between different species within the grass family. Integration of the genetic maps of rice, foxtail millet, sugar cane, sorghum, maize, the Triticeae cereals and oats into a single synthesis reveals that some chromosome arrangements characterise taxonomic groups, while others have arisen during or after speciation. A detailed analysis of the comparative maps of seven species, belonging to three subfamilies, and their applications are described below.     

Resurrection grasses in India

Summary A search for desiccation tolerant grasses in India revealed nine grass species (in the genera Eragrostiella, Oropetium and Tripogon) whose ability to recover from airdryness had not previously been reported. Dry leaves of these species recover uninjured within 24 h of plants receiving water. Desiccation tolerance limits were 0%–11% RH (at 28°C). Some species were relatively tall and vigorous and may be useful for grazing purposes in arid areas.     

Mutator transposase is widespread in the grasses

Although the Mutator (Mu) system is well characterized in maize (Zea mays), very little is known about this highly mutagenic system of transposons in other grasses. Mutator is regulated by the MuDR class of elements, which encodes two genes, one of which, mudrA, has similarity to a number of bacterial transposases. Experiments in our laboratory, as well as database searches, demonstrate that mudrA sequences are ubiquitous and diverse in the grasses. In several species it is clear that multiple paralogous elements can be present in a single genome. In some species such as wheat (Triticum aestivum) and rice (Oryza sativa), mudrA-similar sequences are represented in cDNA databases, suggesting the presence of active Mu transposon systems in these species. Further, in rice and in sorghum, mudrA-like genes are flanked by long terminal inverted repeats, as well as the short host sequence direct repeats diagnostic of insertion. Thus, there is ample evidence that systems related to Mu in maize are at least potentially active in a wide variety of grasses. However, the mudrB gene, though important for Mu activity in maize, is not necessarily a component of Mu elements in other grasses.     

Anthocyanins of grasses

The anthocyanin content of 23 grass species (Poaceae) belonging to five subfamilies has been determined. Altogether 11 anthocyanins were identified; the 3-(6″-malonylglucosides) and 3-glucosides of cyanidin, peonidin and delphinidin, the 3-(3″,6″-dimalonylglucoside), 3-(6″-rhamnosylglucoside) and 3-(6″-glucosylglucoside) of cyanidin, in addition to peonidin 3-(dimalonylglucoside) and delphinidin 3-(6″-rhamnosylglucoside). Anthocyanins acylated with one and/or two malonic acid moieties dominated the anthocyanin profiles of all the species in the subfamilies Pooideae and Panicoideae. On the other hand, the 3-glucoside and 3-rutinoside of cyanidin were the major anthocyanins in Sinarundinaria murielae (subfamily Bambusoideae) and Molinia caerulea (subfamily Arundinoideae), while the 3-glucosides of cyanidin and peonidin were the principal anthocyanins in rice, Oryza sativum (subfamily Oryzoideae). Pelargonidin derivatives and free anthocyanidins have previously been reported to occur in several Poaceae species, however, not identified in any of the species included in this survey.     

Attacking invasive grasses

In grasslands fire may play a role in the plant invasion process, both by creating disturbances that potentially favour non‐native invasions and as a possible tool for controlling alien invasions. Havill et al. (Applied Vegetation Science, 18, 2015, this issue) determine how native and non‐native species respond to different fire regimes as a first step in understanding the potential control of invasive grasses.     

Attribute correlations in the Poaceae (grasses)

Investigation of correlations between a number of two-state attributes for a sample of grass genera revealed that a high proportion of the correlations were statistically significant. There were proportionately more correlations between attributes from the same organ than between attributes from different organS. Furthermore, attributes associated with the fruit and leaf were found to be more closely correlated with attributes other than those of the flower and spikelet, thereby indicating fruit and leaf attributes to be important in the classification of the grasseS. It is considered that the correlations have arisen in part as a result of the phylogenetic origins of the genera and in part as a response to natural selection determining distribution of genera adapted to present-day habitats.     

Comparative morphology of lodicules in grasses

Lodicules are basically peltate-ascidiate phyllomes, as are many other perianth appendages in Monocotyledons. Their structure is especially obvious in Zea and several Andropogonoideae and Panicoideae. In various genera of the Panicoideae and in Oryza they are fundamentally ascidiate but longitudinally split on their distal sides. Lodicules of the Festucoideae, with their dorsal wings, are easily derived from the latter, and so are probably at least some bambusoid lodicules. These findings lend support to the classical interpretation of lodicules as discrete perianth appendages.     

Comparative ultrastructure of microhairs in grasses

Ultrastructure of microhairs is described for 17 species of Poaceae, involving four subfamilies and the 'chloridoid', 'panicoid' and 'Enneapogon' morphological types. The plasma membrane invaginations known as partitioning membranes implicated in salt secretion were found in the basal cells of only some of the 'chloridoid type' microhairs. They were absent from 'panicoid type' microhairs, but present in the cap cells of the 'Enneapogon type'. Characteristics common to known secretory tissues, however, were observed in all microhairs studied, implying secretory activity in all the morphological types.     

Additional chromosome counts in Nigerian grasses

Chromosome counts are presented for 43 collections of Nigerian grasses representing 39 species and 25 genera.     

Summer dormancy in perennial temperate grasses

BACKGROUND AND AIMS: Dormancy has been extensively studied in plants which experience severe winter conditions but much less so in perennial herbaceous plants that must survive summer drought. This paper reviews the current knowledge on summer dormancy in both native and cultivated perennial temperate grasses originating from the Mediterranean Basin, and presents a unified terminology to describe this trait. SCOPE: Under severe drought, it is difficult to separate the responses by which plants avoid and tolerate dehydration from those associated with the expression of summer dormancy. Consequently, this type of endogenous (endo-) dormancy can be tested only in plants that are not subjected to moisture deficit. Summer dormancy can be defined by four criteria, one of which is considered optional: (1) reduction or cessation of leaf production and expansion; (2) senescence of mature foliage; (3) dehydration of surviving organs; and (4, optional) formation of resting organs. The proposed terminology recognizes two levels of summer dormancy: (a) complete dormancy, when cessation of growth is associated with full senescence of foliage and induced dehydration of leaf bases; and (b) incomplete dormancy, when leaf growth is partially inhibited and is associated with moderate levels of foliage senescence. Summer dormancy is expressed under increasing photoperiod and temperature. It is under hormonal control and usually associated with flowering and a reduction in metabolic activity in meristematic tissues. Dehydration tolerance and dormancy are independent phenomena and differ from the adaptations of resurrection plants. CONCLUSIONS: Summer dormancy has been correlated with superior survival after severe and repeated summer drought in a large range of perennial grasses. In the face of increasing aridity, this trait could be used in the development of cultivars that are able to meet agronomic and environmental goals. It is therefore important to have a better understanding of the genetic and environmental control of summer dormancy.     

Alkaloid toxins in endophyte-infected grasses.

Grasses infected with clavicipitaceous fungi have been associated with a variety of diseases including classical ergotism in humans and animals, fescue foot and summer syndrome in cattle, and rye-grass staggers in sheep. During the last decade it has been recognized that many of these fungal infections are endophytic; a fungal endophyte is a fungus that grows entirely within the host plant. Inspection of field collections and herbarium specimens has revealed that such infections are widespread in grasses. The chemistry associated with these grass-fungal interactions has proved to be interesting and complex, as each grass-fungal pair results in a unique "fingerprint" of various alkaloids, of which some are highly toxic to herbivores. In many cases the presence of an endophyte appears to benefit the plant by increasing drought resistance, or by increasing resistance to attack by insects, thus improving the overall survivability of the grass. This review will focus on alkaloids that have been reported in endophyte-infected grasses.     

Invasive grasses and native Asteraceae in the Brazilian Cerrado

Anthropogenic disturbances frequently modify natural disturbance regimes and foster the invasion and spread of nonindigenous species. However, there is some dispute about whether disturbance events or invasive plants themselves are the major factors promoting the local extinction of native plant species. Here, we used a set of savanna remnants comprising a gradient of invasive grass cover to evaluate whether the species richness of Asteraceae, a major component of the Brazilian Cerrado, is affected by invasive grass cover, or alternatively, whether variation in richness can be directly ascribed to disturbance-related variables. Furthermore, we evaluate whether habitat-specialist Asteraceae differ from habitat generalist species in their responses to grass invasion. Abundance and species richness showed unimodal variation along the invasive grass gradient for both total Asteraceae and habitat-generalists. The cerrado-specialist species, however, showed no clear variation from low-to-intermediate levels of grass cover, but declined monotonically from intermediate-to-higher levels. Through a structural equation model, we found that only invasive grass cover had significant effects on both abundance and species density of Asteraceae. The effect of invasive grass cover was especially high on the cerrado-specialist species, whose proportion declined consistently with increasing invasive dominance. Our results support the prediction that invasive grasses reduce the floristic uniqueness of pristine vegetation physiognomies.     

Multiple genetic pathways for seed shattering in the grasses

Shattering is an essential seed dispersal mechanism in wild species. It is believed that independent mutations at orthologous loci led to convergent domestication of cereal crops. To investigate genetic relationships of Triticeae shattering genes with those of other grasses, we mapped spike-, barrel- (B-type), and wedge-type (W-type) spikelet disarticulation genes in wheat and its wild relatives. The Br1 gene for W-type disarticulation was mapped to a region delimited by Xpsr598 and Xpsr1196 on the short arm of chromosomes 3A in Triticum timopheevii and 3S in Aegilops speltoides. The spike- and W-type disarticulation genes are allelic at Br1 in Ae. speltoides. The B-type disarticulation gene, designated as Br2, was mapped to an interval of 4.4 cM between Xmwg2013 and Xpsr170 on the long arm of chromosome 3D in Aegilops tauschii, the D-genome donor of common wheat. Therefore, B- and W-type disarticulations are governed by two different orthologous loci on group-3 chromosomes. Based on map position, orthologs of Br1 and Br2 were not detected in barley, maize, rice, and sorghum, indicating multiple genetic pathways for shattering in grasses. The implications of the mapping results are discussed with regard to the evolution of polyploid wheat and domestication of cereals.Supplementary material is available in the online version of this article at