The dynamic ups and downs of genome size evolution in Brassicaceae

Crucifers (Brassicaceae, Cruciferae) are a large family comprisingsome 338 genera and c. 3,700 species. The family includes importantcrops as well as several model species in various fields ofplant research. This paper reports new genome size (GS) datafor more than 100 cruciferous species in addition to previouslypublished C-values (the DNA amount in the unreplicated gameticnuclei) to give a data set comprising 185 Brassicaceae taxa,including all but 1 of the 25 tribes currently recognized. Evolutionof GS was analyzed within a phylogenetic framework based ongene trees built from five data sets (matK, chs, adh, trnLF,and ITS). Despite the 16.2-fold variation across the family,most Brassicaceae species are characterized by very small genomeswith a mean 1C-value of 0.63 pg. The ancestral genome size (ancGS)for Brassicaceae was reconstructed as ^anc1C = 0.50 pg. Approximately50% of crucifer taxa analyzed showed a decrease in GS comparedwith the ancGS. The remaining species showed an increase inGS although this was generally moderate, with significant increasesin C-value found only in the tribes Anchonieae and Physarieae.Using statistical approaches to analyze GS, evolutionary gainsor losses in GS were seen to have accumulated disproportionatelyfaster within longer branches. However, we also found that GShas not changed substantially through time and most likely evolvespassively (i.e., a tempo that cannot be distinguished betweenneutral evolution and weak forms of selection). The data revealan apparent paradox between the narrow range of small GSs overlong evolutionary time periods despite evidence of dynamic genomicprocesses that have the potential to lead to genome obesity(e.g., transposable element amplification and polyploidy). Toresolve this, it is suggested that mechanisms to suppress amplificationand to eliminate amplified DNA must be active in Brassicaceaealthough their control and mode of operation are still poorlyunderstood.     

Nucleic Acid, Protein, and Starch Synthesis in Developing Cotyledons of Pisum arvense L.

During the cell-division period of cotyledon development inPisum arvense L. cell volume increases slightly but nuclearvolume shows little variation and the DNA content remains atthe 2C to 4C level. During the main period of cell expansionthere is a close correlation between cell volume, nuclear volume,and nuclear DNA content, the nuclei of the largest storage cellsfinally attaining the 64C level. The rate of RNA synthesis increasesseveral days after the increase in DNA has begun and at thesame time accumulation of reserve protein and starch begins.RNA and starch synthesis apparently cease some time before maturationbut protein synthesis continues until the seeds are ripe. Cotyledondevelopment was found to comprise two distinct phases: an initialphase of cell division and differentiation during which DNA,RNA, and protein per unit volume of cell decline; and a phaseof reserve accumulation in which DNA per unit volume of cellremains constant but RNA and protein per unit volume increase,starch synthesis is initiated, and all the cotyledon cells assumethe properties of storage cells.     

Intergeneric and Interspecific Relationships in Araceae tribe Caladieae and Development of Molecular Markers using Amplified Fragment Length Polymorphism (AFLP)

Since amplified fragment length polymorphism (AFLP) analysishas proved useful in distinguishing cultivars of Caladium, itwas used to assess the status of species of Caladium vs. Xanthosoma,both in tribe the Caladieae, and to reassess the position ofHapaline in the same tribe. AFLP analysis using three primercombinations was carried out on four species of Caladium(C.bicolor, C. humboldtii, C. lindenii and C. schomburgkii). Resultsshowed that AFLP can distinguish between the different speciesby their unique and different banding patterns. AFLP analysisconfirmed that C. humboldtii is a species distinct from C. bicolorand that C. lindenii is a true Caladium species and does notbelong to Xanthosoma. UPGMA cluster analysis showed that C.bicolor and C. schomburgkii are most similar and that C. humboldtiiis closer to the C. bicolor / C. schomburgkii cluster comparedwith C. lindenii. Genetic relationships between Caladium, Xanthosoma,Hapaline, Alocasia and Protarum were also examined by AFLP analysisusing eight primer combinations. Several useful molecular markerswere specific either to Caladium orXanthosoma , so that AFLPcan be used to distinguish species of these two genera. Geneticanalysis of the genera examined confirms that the Caladieaeand Colocasieae tribes are distinct and that Hapaline fallswithin the tribe Caladieae and that Protarum is most distantfrom all the genera examined. Copyright 2000 Annals of BotanyCompany Araceae, Caladium, Xanthosoma, Hapaline, Alocasia, Protarum, AFLP DNA fingerprinting, diversity, AFLP markers     

Ultrastructural Observations on Proliferating Storage Cells of Mature Cotyledons of Phaseolus vulgaris L. Cultured in vitro

Explants of mature cotyledons of Phaseolus vulgaris form callusrapidly when cultured in vitro with their adaxial surfaces embeddedin a solidified nutrient medium containing coconut milk, kinetinand 2,4-D. Proliferation is confined to the highly polyploidstorage cells and commences near the adaxial epidermis, whichis soon ruptured by the callus developing internally. Callusformation progresses to the abaxial tissue and within 3–4weeks sub-culturing is possible. The in vitro grown storage cells undergo thinning of their walls,loss of food reserves, hypertrophy, development of various new-wallsand nuclear activation leading to division. The induction ofnuclear and cell divisions within this mature storage tissuecontrasts with normal germination in which these cells undergorapid senescence after depletion of their food reserves. Nuclear division in early callus growth is apparently mainlyamitotic. It is preceded by the development of multiple nucleoli.The nuclear envelope also becomes more complex and deeply lobed;leading to formation of a nuclear isthmus and final separationinto two nuclei. No chromosomes are visible during nuclear fragmentation.Amitosis is accompanied by freely-forming walls, which may developadjacent to a nuclear isthmus and perhaps participate in nuclearfragmentation. Large labyrinthine wall bodies frequently occuron these walls. Mitoses are only observed in already dividedstorage cells. A cell plate forms between the two daughter nuclei,and microtubules are present at its margins in contrast to freely-formingwalls where none are evident. Phaseolus vulgaris L., bean, in-vitro culture, cotyledon, ultrastructure     

小腹茧蜂亚科的雄外生殖器及族级单元系统发育的研究

对分布在东洋区和古北区的小腹茧蜂亚科 (膜翅目: 茧蜂科)21个属的67个种及外群折脉茧蜂属 (膜翅目: 茧蜂科) 2个种的雄外生殖器的5个性状进行了比较研究。在形态学研究的基础上,通过选用头部、胸部和腹部(包括雌雄外生殖器的性状) 等34个性状,运用支序分析的方法探讨了分布在东洋区和古北区的小腹茧蜂亚科21个属以及它们所属的族间的系统发育关系,并对Mason (1981) 的分类系统进行了重新评价。雄外生殖器和支序分析基本上证实并恢复了由Mason (1981) 确定的2个主要分支,即绒茧蜂族Apantelini+小腹茧蜂族Microgastrini和拱茧蜂族Fornicini+盘绒茧蜂族Cotesiini+侧沟茧蜂族MicroplitinI。绒茧蜂族Apantelini、拱茧蜂族Fornicini和侧沟茧蜂族Microplitini为单系群也被支持,但小腹茧蜂族Microgastrini和盘绒茧蜂族Cotesiini是否为单系群尚难于在树形图中体现,而且族内各属间的分支关系有变动。因此,尽管Mason的族级分类单元有一些欠缺,但仍是可信、实用的,不同意Walker等 (1990) 认为不应再使用Mason分族系统的观点。     

The features of cotyledon areoles in Leguminosae and their systematic utility

The cotyledon areole, which is a spot with granular projections of epidermal cells, appears on the abaxial surface and on the midvein of some legume seed cotyledons. The distribution and systematic utility of cotyledon areoles were studied by observation of 132 legume species, which represent 100 genera and are classified into 34 tribes of three subfamilies, i.e., Caesalpinioideae, Mimosoideae, and Papilionoideae. The cotyledon areole is found in many species of Papilionoideae but not in the other two subfamilies. Presence of a cotyledon areole is presumed to be an apomorphic character state in Papilionoideae from the outgroup rule.     

Analysis of phylogenetic relationships of Brassicaceae species based on Chs sequences

Sequences of nuclear chalcone synthase gene (Chs) were analyzed for species of the Brassicaceae family to reconstruct phylogenetic relationships. The phylogeny for 106 species of 60 genera was reconstructed, and assigned to 24 tribes, using maximum parsimony, maximum likelihood, and neighbor-joining methods. Most of the tribes can be assigned to the major lineages (Lineages I–III) suggested by Beilstein et al. (2006). The tribe Camelineae was not monophyletic. Conringia planisiliqua together with Orychophragmus violaceus would not be recognized as a new tribe proposed by the previous studies, and C. planisiliqua should be a member of tribe Isatideae. The genera delimitation and monophyly of the expanded Solms-laubachia were also confirmed by our data. Furthermore, one parent of inter-tribal allopolyploid Pachycladon appeared to be most closely associated with Crucihimalaya, Transberingia and tribes Boechereae and Halimolobeae, another parent was proved to be in tribe Smelowskieae.     

Stalked Glandular Hairs in the Pappophoreae (Gramineae)

Stalked glandular hairs on the vegetative parts of grasses areapparently confined to the tribe Pappophoreae. They have beenrecorded from three of the genera in this tribe, Enneapogon,Schmidtia, and Kaokochloa; the first occurs mainly in the OldWorld and the remaining two in Africa only. The hairs are absentfrom one of the genera (Pappophorum) confined to the New World,but investigation showed that they are present in the other(Cottea).     

Phylogeny and morphological evolution of tribe Menispermeae (Menispermaceae) inferred from chloroplast and nuclear sequences

The Menispermaceae family contains ca. 72 genera with 450 species that are almost entirely tropical. Its phylogeny at the tribal level has never been examined using molecular data. Here we used DNA sequences of the chloroplast matK gene and trnL-F regions, and the nuclear ITS region to study the delimitation and position of the tribe Menispermeae within the family and its subtribal monophyletic groups. Family-wide phylogenetic analyses of the chloroplast data produced two strongly supported clades. The first clade contains two subclades: Coscinieae including Arcangelisia and Anamirta, and Tinosporeae sensu lato including Fibraureae, supported by morphological characters, such as traits of the cotyledon, stylar scar and embryo. The second clade consists of the tribes Menispermeae sensu DC. and Tiliacoreae Miers. All our analyses surprisingly recognized that tribe Menispermeae is not monophyletic unless tribe Tiliacoreae is included, suggesting that characters of cotyledon and stylar scar are very important for the infrafamilial classification, and that endosperm presence vs. absence was over-emphasized in traditionally tribal division of the family. Our topologies indicate a secondary loss of endosperm. The monophyly of two subtribes of the tribe Menispermeae, Stephaniinae and Cissampelinae, is supported by the cpDNA and ITS data, as well as by morphological characters, including aperture types and shapes, and colpal membrane features of pollen grains, and sepal number of male flowers. The Cocculinae was recognized as a paraphyletic group containing the remaining genera of the tribe Menispermeae.     

Nuclear Dry Mass and Area in Epidermal Cells of Senescing Soybean Cotyledons

The nuclear dry mass and area of epidermal cells of senescingsoybean cotyledons were measured with an interference microscopeand found to decrease until cotyledon abscission. Decapitationafter germination prevented yellowing and abscission of cotyledonsand the decrease of both nuclear dry mass and area. The meansof nuclear dry mass and area for normal and decapitated cotyledonswere highly correlated in two experiments, r=0.0.76 and 0.90respectively.     

Nuclear Changes in the Cotyledons of Pisum arvense L. during Germination

In the cells of the cotyledons of Pisum arvense L. there isa close correlation between cell volume, nuclear volume, andnuclear DNA level. The cells of the epidermis are at the 2Clevel of DNA, those of the hypodermus vary from 2C to 4C, whilethose of the storage tissues range from 4C to 16C. During germinationthe nucler increase in size In the storage tissues there isa three to fourfold increase, which is accompanied by an increasein lobing of the nucler Simultaneously the DNA level of thenucler decreases by about 50 per cent. There are parallel changesin nuclear histone levels. Initially nuclear RNA level is lowbut in any given cell it increases to a maximum at the timethe storage reserves of the cell begin to disappear, after whichit declines. The level of cytoplasmic RNA is high initiallyin the tissues at the abaxial side of the cotyledon. Duringthe first few days of germination it declines until the over-alllevel is uniformly low, after which there is a further smalldecline.     

Karyological Anatomy of Fibre Development in the Leaves of Agave americana L. var. marginata alba Trel.

From a study of 100 metaphase plates in root-tip squashes and75 fibre-cells in leaf-base squashes, it is found that the chromosomenumber, although having an irregular type of variation, commonlytend to occur as multiples of 15, the haploid number. In developingfibre-cells the tendency of complete endomitosis (resultingin 2n, 4n, and 8n numbers) is stronger than the partial endomitosis(resulting in 5n, 6n, 7n, etc.). Nuclear volumes of fibre-cellsalso roughly correspond to 2K, 4K, and 8K. Significant linearcorrelations between chromosome number and nuclear volume andbetween nuclear volume and fibre-cell volume has been obtained.Thus the development and differentiation of fibres involve completeand partial endomitoses, accompanied by somatic non-disjunctionphenomena.     

Phylogeny of the Braconinae (Hymenoptera: Braconidae): A new tribal order!

Generic relationships within the parasitoid wasp subfamily Braconinae are assessed based on a molecular phylogenetic analysis of four gene fragments: mitochondrial cytochrome c oxidase subunit I, 16S rDNA, nuclear 28S D2-D3 rDNA and elongation factor 1-alpha. Our results support the recognition of Aphrastobraconini, Braconini and Coeloidini plus three new tribes: Compsobraconini tribus nov ., Tropobraconini tribus nov . and Virgulibraconini tribus nov . The first of these new tribes is restricted to the New World; the second includes the Old World genera Tropobracon Cameron, Trispinaria Quicke and Grangerbracon Samartsev and Belokobylskij and possibly others, whereas the third comprises the Australian genus Virgulibracon Quicke, plus several other described and undescribed Australian genera. Consistent placement of Amyosoma Viereck with members of the Virgulibraconini tribus nov . is discussed, whereas Amyosoma is left currently unplaced. A preliminary key to tribes is presented, and the characters used to differentiate between Aphrastobraconini and Braconini are revised. Megacoeloides Quicke was never recovered with Coeloides, the type genus of Coeloidini, so it is treated as Braconinae incertae sedis. By combining molecular and morphological traits, nearly all valid genera are assigned to tribes, and the possible relationships of the remainder are discussed. Alienoclypeus Shenefelt, 1978 is synonymised with Atanycolus Förster, 1862 (Atanycolus insolitus (Shenefelt) comb. nov .). Several new genera have been revealed and will be described elsewhere.     

Self-incompatibility in the Commelinaceae

This paper reports on a survey of self-incompatibility in 110species of 22 genera in the family Commelinaceae. Genera fromboth tribes, Tradescantieae and Commelineae are included. Fifty-fivespecies were found to be self-incompatible, 50 species self-compatible,and five species comprised individuals which were self-incompatibleand individuals which were self-compatible. This variabilityand its possible evolutionary significance are discussed. Self-incompatible species had actinomorphic flowers and themajority of these were in the Tradescantieae. Species with zygomorphicflowers which were more commonly found in the Commelineae wereself-compatible. The ubiquitous presence of binucleate pollengrains supports previous data that self-incompatibility is ofthe gametophytic type. The site of pollen tube arrest, however,was on the stigma at or near the base of the stigma papillacells. There were two exceptions to this viz. an unnamed Dichorisandraspecies and Siderasis fuscata where pollen tube arrest was stylar. The significance of these data to taxonomy also receives comment. Commelinaceae, incompatibility, self-compatibility     

The evolution of egg size in the brood parasitic cuckoos

We compared genera of nonparasitic cuckoos and two groups ofparasitic cuckoos: those raised together with host young ("nonejectors")and those in which the newly hatched cuckoo either ejects thehost eggs or chicks, or kills the host young ("ejectors"). Nonejectorsare similar to their hosts in body size and parasitize largerhosts than do ejectors, which parasitize hosts much smallerthan themselves. In both types of parasite, the cuckoo's eggtends to match the host eggs in size. To achieve this, nonejectorshave evolved a smaller egg for their body size than have nonparasiticcuckoos, and ejectors have evolved an even smaller egg. Amongejector cuckoo genera, larger cuckoos have larger eggs relativeto the eggs of their hosts, and the relationship between cuckooegg volume (mass of the newly-hatched cuckoo) and host egg volume(mass to be ejected) did not differ from that predicted by weight-liftingallometry. However, comparing among Cuculus cuckoo species,the allometric slope differed from the predicted, so it is notclear that egg size is related to the need to give the cuckoochick sufficient strength for ejection. Comparing the two mostspeciose ejector genera, Chrysococcyx cuckoos (smaller and parasitizedome-nesting hosts) lay eggs more similar in size to their host'seggs than do Cuculus cuckoos (larger and parasitize open cup–nestinghosts). Closer size-matching of host eggs in Chrysococcyx mayreflect the following: (1) selection to reduce adult body massto facilitate entry through small domed nest holes to lay, and(2) less need for a large egg, because longer incubation periodsin dome-nesting hosts allow the young cuckoo more time to growbefore it need eject host eggs.     

An Analysis of Seed Development in Pisum sativum: IV. COTYLEDON CELL POPULATIONS IN VIVO AND IN VITRO

A method for quantifying changes in the cell population of Pisumsativum cotyledons during development is described. The methodis based on determining the frequency distribution for cellarea following the random sampling of a single-cell suspensionof cotyledon cells. The population profile of these cells changedprogressively and systematically from a single population, similarin size to meristematic cells, found in embryos less than 3.0mg in fresh weight, to a bimodal population in embryos greaterthan 100 mg fresh weight. This method was used to compare embryosof similar size from two genotypes near-isogenic except forgenes at the r locus. No significant differences were foundbetween the cell population profiles of embryos up to 30 mgfresh weight. However, a significant difference was found betweenembryos with fresh weights of 100 mg, the wrinkled (rr) linehaving a higher mean and maximum cell area (2 951 µm²and 9 240 µm² respectively) than the round (RR) line (2591µm²and 6470 µm²respectively). Comparisons were alsomade between cotyledon cell populations from round (RR) embryosgrown in vivo and in vitro. The most obvious differences werethe higher mean and maximum cell size of the large cell populationof in vitro grown embryos which were twice those found in vivo.Embryos grown to either 30 mg or 100 mg fresh weight in vitrohad a much greater proportion of large cells in the populationwith a corresponding reduction in total cotyledon cell number,compared with similar sized embryos grown in vivo. These data suggest that comparisons between different genotypes,or, between cultured and in vivoembryos, based on morphologicalsimilarities between embryos, may be invalid and subject tomisinterpretation. Key words: Pea, seed development, cell population     

Closing the gaps: phylogenetic relationships in the Brassicaceae based on DNA sequence data of nuclear ribosomal ITS region

Sequence data from the nuclear encoded ribosomal internal transcribed spacer (ITS) region were used to determine monophyly of tribes, tribal limits, and tribal relationships of 96 so far unassigned or tentatively assigned genera (represented by 101 taxa/accessions) within the Brassicaceae. Maximum-parsimony and maximum-likelihood analyses of 185 ITS Brassicaceae sequences, which also included representatives of each of the 34 currently recognized tribes, supported the separate phylogenetic distinctness of these tribes and permitted the tribal assignment of all but 12 of the unassigned genera into tribal clades. The data support the recognition of eight new, well-resolved, uni- or oligogeneric tribes recognized herein as the Alyssopsideae [96% bootstrap support (BS); including the central and southwestern Asian Alyssopsis and Calymmatium], Asteae (100% BS; including the Mexican Asta), Eudemeae (97% BS; South American Brayopsis, Eudema, and Xerodraba), Kernereae (96% BS; European Kernera and Rhizobotrya), Notothlaspideae (100% BS; New Zealandic Notothlaspi), Oreophytoneae (100% BS; eastern African Oreophyton and southern European Murbeckiella), and Yinshanieae (100% BS; Chinese Yinshania), as well as the moderately supported Microlepidieae (75% BS; Australian Microlepidium and Carinavalva). Furthermore, the results fully support the recent findings that the tribes Schizopetaleae and Thelypodieae ought to be recognized as two distinct tribes instead of a single tribe, as well as provide some support for the re-establishment of the tribe Cremolobeae, bringing the total number to 44 tribes in the family. Nearly 92% (308) of the 336 genera in the family have been assigned to a tribe. The earlier-published Anastaticeae is taken here to replace the Malcolmieae.     

Composition, Degradation and Utilization of Endosperm During Germination in the Oil Palm (Elaeis guineensis Jacq.)

The insoluble carbohydrate and lipid fractions, and -D-galactosidase,ß-D-mannosidase and isocitrate lyase activities werestudied in the various tissues of oil palm (Elaeis guineensisJacq.) kernels prior to and during germination. In ungerminatedkernels insoluble carbohydrate and lipid constituted 36 and47% of endosperm dry weight respectively. During germinationthe thick endosperm cell walls became markedly thinner, concurrentwith a significant decrease in the percentage of insoluble carbohydrateand an increase in -galactosidase and ß-mannosidaseactivity in both degraded and residual endosperm. The proportionof lipid in degraded endosperm also increased significantly.The insoluble carbohydrate appears to be a galactomannan locatedin the secondary walls of the endosperm. No galactomannan wasdetected in oil palm embryos or haustoria. Isocitrate lyasewas present in, and confined to, tissues of the haustorium ofgerminating kernels. The enzyme was not active in endospermat any stage of germination, nor was it active in embryos beforeor at the end of imbibition. The results suggest that galactomannan is the second largestcomponent of oil palm endosperm and that it is utilized morerapidly than lipid during the early stages of germination. Thefact that isocitrate lyase activity is confined to the haustoriumsuggests that in Elaeis gluconeogenesis, the conversion of triglycerideto carbohydrate, takes place entirely within the cotyledon ofthe seed. Elaeis guineensis, galactomannan, galactosidase, germination, isocitrate lyase, mannosidase, oil palm     

Gas Chromatography-Flame Thermionic Detector Analysis of Cytokinins in Etiolated Squash Seedlings using 14C-BA as an Internal Standard

Cytokinin contents in cotyledon, hypocotyl and root of etiolatedsquash (Cucurbita maxima Duch.) seedlings were determined byinstrumental analysis using ¹⁴C-benzyladenine (¹⁴C-BA) as aninternal standard. Crude extracts were purified using insolublepolyvinylpyrrolidone, cellulose-phosphate column and SEP-PAKC18 cartridge, then applied to a Sephadex LH-20 column to separatezeatin riboside (ZR), isopentenyl adenosine, isopentenyl adenine,¹⁴C-BA and a mixture of zeatin (Z) and dihydrozeatin (DHZ).The recovery rate for the cytokinin fractions after LH-20 wascorrected by ¹⁴C-BA. Each cytokinin fraction was further purifiedby HPLC which also separated Z and DHZ in the LH-20 fraction.Before permethylation, ¹⁴C-BA was added to each of the cytokininfractions to correct the methylation rates. Each methylatedcytokinin fraction was again purified by HPLC, then subjectedto gas chromatography with a capillary column and flame thermionicdetector. The detection limit of cytokinins by this system was0.1 ng. cis-ZK was the most abundant cytokinin in all tissues of theetiolated squash seedlings. Active cytokinins such as trans-ZRand trans-Z were mostly found in cotyledons with lesser amountsin the roots. DHZ was most abundant in the cotyledon. All cytokininsisolated by this procedure were confirmed by gas chromatographyselectedion monitoring. (Received December 26, 1986; Accepted June 1, 1987)     

Cytochrome c activates K+ channels before inducing apoptosis

Cellshrinkage is an early prerequisite for apoptosis. Theapoptotic volume decrease is due primarily to loss ofcytoplasmic ions. Increased outward K⁺ currents have indeedbeen implicated in the early stage of apoptosis in many celltypes. We found that cytoplasmic dialysis of cytochrome c(cyt-c), a mitochondria-dependent apoptotic inducer,increases K⁺ currents before inducing nuclear condensationand breakage in pulmonary vascular smooth muscle cells. Thecyt-c-mediated increase in K⁺ currents tookplace rapidly and was not affected by treatment with a specificinhibitor of caspase-9. Cytoplasmic dialysis of recombinant (active)caspase-9 negligibly affected the K⁺ currents. Furthermore,treatment of the cells with staurosporine (ST), an apoptosisinducer that mediates translocation of cyt-c frommitochondria to the cytosol, also increased K⁺ currents,caused cell shrinkage, and induced apoptosis (determined byapoptotic nuclear morphology and TdT-UTP nick end labeling assay).The staurosporine-induced increase in K⁺ currents concurredto the volume decrease but preceded the activation of apoptosis(nuclear condensation and breakage). These results suggest that thecyt-c-induced activation of K⁺ channels and theresultant K⁺ loss play an important role in initiating theapoptotic volume decrease when cells undergo apoptosis.