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Caryopsis !FULL!

The term grain is also used in a more general sense as synonymous with cereal (as in "cereal grains", which include some non-Poaceae). Considering that the fruit wall and the seed are intimately fused into a single unit, and the caryopsis or grain is a dry fruit, little concern is given to technically separating the terms fruit and seed in these plant structures. In many grains, the "hulls" to be separated before processing are flower bracts.


The name "caryopsis" is derived from the Greek words karyon and -opsis, meaning "nut" and "having the appearance of", respectively. The term was first used by Achille Richard to refer to the dry, monospermic, indehiscent fruit commonly found in grasses.[3]

This definition of fruit for the Gramineae family has persisted to the modern day, but some botanists have challenged the idea that the dry caryopsis is a defining characteristic of the family. The other forms of fruit proposed to be borne by grasses include achenes,[4] utricles,[4] berries,[5] and nuts.[6] However, others have suggested that these differing fruit structures are representative of caryopsis diversity rather than of entirely different structures.[7] This diverse form of the caryopsis would include the follicle-like form of Crypsis and Eleusine where a free pericarp adjoins the seeds which are extruded when moistened (as in an achene or utricle), the berry-like form found in some bamboo genera including Dinochloa and Olmeca where the pericarp is more thick and fleshy, and the nut-like form found in Dendrocalamus and Schizostachyum. By this definition, the caryopsis is truly the only fruit type found in the Gramineae. The types of caryopsis are often distinguished by the terms "modified caryopsis", referring to caryopses with a pericarp not wholly adnate to the seed coat, and "true caryopsis", referring to those with a pericarp totally adherent to the seed coat.[8]

Once these babies are in the ground, they already have everything they need to get growing. The DNA inside a caryopsis will trigger the process, with specific parts of its insides starting to push out, and receiving all the additional help it needs from other genetic material inside the seed.

Degeneration of various maternal tissues in rice caryopsis at different time points Each box represents 1 day. Boxes filled with dark green indicate cells that are alive, boxes filled with pale green indicate cells undergoing gradual degeneration, and empty boxes represent cells that are completely degenerated.

Warm conditions pre-anthesis decreased the quality of husk adhesion, and consequently increased the incidence of grain skinning. Cool post-anthesis conditions further decreased the quality of husk adhesion. The composition of the cementing layer, rather than its structure, differed with respect to husk adhesion quality. This cementing layer was produced at the late milk stage, occurring between nine and 29 days post-anthesis, conditional on the temperature-dependent growth rate. The compounds octadecanol, tritriacontane, campesterol and β-sitosterol were most abundant in caryopses with high-quality husk adhesion. The differences in adhesion quality were not due to incompatible husk and caryopsis dimensions affecting organ contact.

This study shows that husk-to-caryopsis adhesion is dependent on cementing layer composition, and implies that this composition is regulated by temperature before, and during grain development. Understanding this regulation will be key to improving husk-to-caryopsis adhesion.

The barley caryopsis comprises the embryo, the starchy endosperm and the outer aleurone endosperm, surrounded in turn by the nucellar layer, the testa (seed coat), and the pericarp (fruit coat). The outer husk is composed of two glumes, namely the lemma on the dorsal side of the grain, and the palea on the ventral side of the grain [5, 6]. It has been hypothesised that physical damage to malting barley grains, including grain skinning, may be exacerbated by changes in grain length and width, and an incompatibility between grain size and the mechanical strength of the outer husk tissues [7, 8]. Physical contact between the caryopsis and the husk could be expected to differ with changes in grain or glume size. Although there are limited data on differential grain development that relate directly to the husk-caryopsis adhesion process, studies on the effects of temperature differences pre- and post-anthesis on husk and caryopsis development are useful to understand how temperature could be used to manipulate differential growth of these organs and therefore contact between the caryopsis and glumes. For example, higher grain weight attained by increased starch accumulation during growth at low temperatures [9] might increase grain dimensions and result in better contact, and therefore adhesion, between the caryopsis and the husk. Conversely, grains with reduced weights caused by high temperature stress [10, 11] might be expected to have reduced husk-caryopsis contact, resulting in poor quality adhesion. Equally, the size of the husk organs would contribute to the capacity for contact between the husk and caryopsis. Indeed, grain size has been postulated to be determined by the physical limitation of the size of the husk [12, 13], potentially due to effects of pre-anthesis temperature on floret growth [14].

This study used differential temperatures during husk and grain development to separately effect changes in husk and grain size, the structure and composition of the surface cuticles and therefore the cementing layer. It was hypothesised that the quality of husk adhesion, and therefore the severity of grain skinning, would be influenced by one or all of the above, and that by measuring these we would gain insight into critical grain and cuticle developmental stages that influence husk-to-caryopsis adhesion.

A separate experiment was done to examine the caryopsis surface after development of the cementing layer using scanning electron microscopy. Plants of Concerto, and the hull-less variety Nudinka, were grown in pots in a glasshouse as described above. Grains from both cultivars were harvested at GS 77, when in covered barley, the caryopsis is sticky to the touch. These grains were then fixed and processed for scanning electron microscopy as described below.

For transmission electron microscopy of husk material, segments (3 mm long 1 mm wide 1 mm thick) were cut from the centre of the lemma, and spanning one vascular bundle from the palea. Segments of the same size were cut from the centre of the dorsal side of the caryopsis, taking care to ensure that the segments excised included all cell layers down to the starchy endosperm, and avoiding the area over the embryo which does not produce a cementing layer. Segments were fixed in 4% (w/v) paraformaldehyde and 2% (w/v) glutaraldehyde in 100 mM sodium 1,4-piperazinediethanesulfonic acid (PIPES) buffer (pH 7.2) for 4 h at room temperature, then overnight (18 h) at 4 C. Fixed tissue was washed three times in 0.1 M sodium cacodylate buffer (pH 7.3) for 10 min each time. Tissue was then post-fixed in 1% osmium tetroxide in sodium cacodylate for 45 min at room temperature, then washed in three 10 min changes of sodium cacodylate buffer. Washed tissue was dehydrated in an aqueous ethanol series (50, 70, 90, and three 100%) for 15 min each step, and then twice in propylene oxide for 10 min each time. Samples were then embedded in TAAB 812 resin (TAAB laboratories, Berks, England). Sections, 1 μm thick, were cut on a Leica Ultracut ultramicrotome (Leica Microsystems, Milton Keynes, UK), stained with 1% aqueous toluidine blue in 1% borax and viewed on a light microscope to select suitable areas for investigation. Ultrathin sections, 60 nm thick, were cut from selected areas, stained in 1% aqueous uranyl acetate and Reynolds lead citrate then viewed in a Philips CM120 BioTwin transmission electron microscope (Philips Electron Optics, Eindhoven, The Netherlands). Images were taken on a Gatan Orius CCD camera (Gatan, Oxon, UK). The thickness of the inner and outer cuticles (palea and lemma), outer cuticle (caryopsis) and cementing layer (whole grain) was measured using the open-source software Image J [46]. The mean thickness of the cuticular layers for each of the three replicate ears was calculated by taking the mean of five measurements from each of five micrographs per replicate.

For scanning electron microscopy, tissue was cut into 4 mm 4 mm segments from the dorsal side of the caryopsis and fixed and dehydrated as above. Samples were dried in a Polaron Critical Point Drier (Quorum Technologies Ltd., Lewes, UK), mounted on aluminium stubs, and sputter coated with 20 nm gold palladium in an Emscope SC500A sputtercoater (Emscope, Kent, UK) before examining with a Hitachi S-4700 scanning electron microscope (Hitachi, Japan).

Development of main shoots and tillers were recorded every few days from booting until ripening and are shown in relation to date of anthesis, which is indicated by a horizontal dotted line in Fig. 1. Ears from plants grown under warm conditions pre-anthesis took an average of 84 days (2184 C days) from sowing until anthesis, whereas ears from plants grown under cold conditions took an average of 105 (1715 C days) days to reach anthesis. Development rates also differed among the four post-anthesis treatments, with plants grown in cool post-anthesis conditions taking longer to reach ripening than those grown in warm post-anthesis conditions. The CC plants took 71 days from anthesis to ripening (1160 C days), the WC plants 87 days (1421 C days), the WW plants 24 days (624 C days) and the CW plants 27 days (702 C days). Across all treatments, the caryopsis became sticky to the touch at GS 77, when the caryopsis is nearing maximum volume. The CC plants took 29 days from anthesis to GS 77 (474 C days), the WC plants 24 days (392 C days), the WW plants 19 days (494 C days) and the CW plants only 9 days (234 C days). These data suggest that the growing conditions pre-anthesis have an influence on the subsequent rate of development, and length of grain-filling period of the caryopsis. The metabolic processes responsible for production of the sticky cementing material are likely to come into play shortly before the caryopsis becomes noticeably sticky, therefore the period between GS 75 and GS 77 is marked by vertical dashed lines in Fig. 1 to indicate the developmental period, and range in days after anthesis, that the critical period for husk adhesion is likely to span. 041b061a72


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