Abstract
High growth temperatures negatively affect soybean (Glycine max (L.) Merr) yields and seed quality. Soybean plants, heat stressed during seed development, produce seed that exhibit wrinkling, discoloration, poor seed germination, and have an increased potential for incidence of pathogen infection and an overall decrease in economic value. Soybean breeders have identified a heat stress tolerant exotic landrace genotype, which has been used in traditional hybridization to generate experimental genotypes, with improved seed yield and heat tolerance. Here, we have investigated the seed protein composition and ultrastructure of cotyledonary parenchyma cells of soybean genotypes that are either susceptible or tolerant to high growth temperatures. Biochemical analyses of seed proteins isolated from heat-tolerant and heat-sensitive genotypes produced under 28/22 °C (control), 36/24 °C (moderate), and 42/26 °C (extreme) day/night temperatures revealed that the accumulation in soybean seeds of lipoxygenase, the β-subunit of β-conglycinin, sucrose binding protein and Bowman-Birk protease inhibitor were negatively impacted by extreme heat stress in both genotypes, but these effects were less pronounced in the heat-tolerant genotype. Western blot analysis showed elevated accumulation of heat shock proteins (HSP70 and HSP17.6) in both lines in response to elevated temperatures during seed fill. Transmission electron microscopy showed that heat stress caused dramatic structural changes in the storage parenchyma cells. Extreme heat stress disrupted the structure and the membrane integrity of protein storage vacuoles, organelles that accumulate seed storage proteins. The detachment of the plasma membrane from the cell wall (plasmolysis) was commonly observed in the cells of the sensitive line. In contrast, these structural changes were less pronounced in the tolerant genotype, even under extreme heat stress, cells, for the most part, retained their structural integrity. The results of our study demonstrate the contrasting effects of heat stress on the seed protein composition and ultrastructural alterations that contribute to the tolerant genotype’s ability to tolerate high temperatures during seed development.
Highlights
Soybean was originally introduced into the United States as a forage crop [1], but has emerged as a preeminent oilseed crop, owing to the high quality and content of oil and protein in the seeds [2]
We examined the accumulation of immunoglobulin heavy chain-binding protein (BiP), a member of HSP70 pfalamyiElayanralinimedrpsaotrurtedasniiedtsertnohtlaeet nifnodcoiumpslpeadrsomovniicntgrreattnhicseucrltuioplmetoram(EneRcep) rpoofrfoisltoienyignbeitnahndaitcspuatlbeajdyecsttheadamt thaoejoahrteasroht losectrkienspscrho[a2tep1i,en2rs2o]mn. iTanyog examine if different growing temperatures had any effect on heat shock protein (HSP) accumulation, gradual increase that coincided with increased temperature (Figure 3B)
We examined the accumulation of immunoglobulin heavy chain-binding protein (BiP), a member of HSP70 family and a resident endoplasmic reticulum (ER) protein that plays naewmlayjosrynrtohlesiznedchparpoeterionnsinangdnteawrgleytinsygnmthiesfsoizldededpprrootteeiinnss faonrddetgargadetaitnigonmbyisftohledpedrotpearosotemines[2f3o]r
Summary
Soybean was originally introduced into the United States as a forage crop [1], but has emerged as a preeminent oilseed crop, owing to the high quality and content of oil and protein in the seeds [2]. Antibodies raised against the soybean β-subunit of β-conglycinin reacted strongly against the 52 kDa protein from the seeds produced at 28/22 ◦C, whereas only a faint reaction was detected at higher temperatures (Figure 1C). The trend in accumulation in SG and TG seed for BBI was very similar to that noted for the β-subunit of β-conglycinin (Figure 1C) These results indicate that the heat-tolerant genotype’s seed proteome was less impacted by seed growth under elevated temperatures compared to the heat-sensitive genotype. A comparison of the protein profile of SG seeds produced under 28/22 ◦C (control) and 42/26 ◦C day/night temperatures revealed striking differences (Figure 2B). Several vacuoles contained numerous PSV, the size and shape of these storage organelles were somewhat distorted Often, these PSVs were larger (greater than 18.5 μm), and exhibited two regions that showed different staining pattern (Figure 4D). FFigiguurere66. .TTrraannssmmisisssioionneeleleccttrroonnmmiiccrrooggrraapphhss ooff ttoolleerraanntt ((AA,Can)danCd) saenndsistievnesi(tBiv,De )(BsoaynbdeaDn)gseonyobtyeapnes gtehnaottywpeersetghraotwwneraet gdriffowernenatttdeimffpereernattuterems.peMraicturorgesr.aMphiscroofgsroaypbhesaonf csootyybleeadnoncosttyhlaetdwonesrethgartowwenreat g3ro6/w24n◦aCt 3(6A/,2B4)°oCr (4A2/a2n6d◦CB)(Cor,D4)2/d2a6y°/Cnig(ChtatnedmDpe)rdaatuyr/ensi.ghNtutmemerpoeursatpurroetse.inNsutmoreargoeuvsapcruootleeisnasntodrlaigpeid vbaocudoielessaraenodbslieprivdedboinditehsesaereceollbs.seNrvoetedthine dthisetsoertceedllas.ppNeoatreanthcee adnidstosirzteedofapprpoetaeirnansctoeraagnedvsaiczueoolefs pirnottehiencsottoyrlaegdeovnaacruyocleelslsinofththeectootlyelreadnotnsaoryybceealnlsgoefntohteyptoelearnadntthseoycboemapnlegteenlootsyspoef ainntdertnhaelcsotmrupctluetreal loosrsgaonfizinatteiornnailnstthruecsteunrsailtiovregganenizoattyiopne ginrotwhne aset n4s2i/t2iv6e◦Cge(nCo,tDy)p,eregsrpoewctnivaelty.42P/2S6V,°pCro(tCeinansdtorDag),e revsapceucotlievse;lyL.BP, SliVp,idprbootdeiiness;tCorWa,gceevllawcuaolll.es; LB, lipid bodies; CW, cell wall
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