Some easily seen structural features of living plant cells are destroyed or badly distorted by most of the common fixatives and embedding media used in plant histology. In stained sections of plant tissues fixed in FAA (formalin-acetic acid-alcohol mixtures) and embedded in paraffin wax, for example, mitochondria and fine transvacuolar strands of cytoplasm are usually not visible. Many structural features such as these can be preserved, however, with suitable fixatives and embedding media. Fixation in non-coagulant fixatives (e.g., osmium tetroxide, acrolein, glutaraldehyde, formaldehyde) and the use of plastics as embedding media is recommended. A method of fixation in acrolein and embedding in glycol methacrylate polymer is described in detail. In a wide range of plant specimens prepared in this way, stained sections 1-3 microns thick showed excellent preservation of tissue and cell structures. 39 references, 11 figures.

Plant microtechnique: some principles and new methods

The testa of higher plant seeds protects the embryo against adverse environmental conditions. Its role is assumed mainly by controlling germination through dormancy imposition and by limiting the detrimental activity of physical and biological agents during seed storage. To analyze the function of the testa in the model plant Arabidopsis, we compared mutants affected in testa pigmentation and/or structure for dormancy, germination, and storability. The seeds of most mutants exhibited reduced dormancy. Moreover, unlike wild-type testas, mutant testas were permeable to tetrazolium salts. These altered dormancy and tetrazolium uptake properties were related to defects in the pigmentation of the endothelium and its neighboring crushed parenchymatic layers, as determined by vanillin staining and microscopic observations. Structural aberrations such as missing layers or a modified epidermal layer in specific mutants also affected dormancy levels and permeability to tetrazolium. Both structural and pigmentation mutants deteriorated faster than the wild types during natural aging at room temperature, with structural mutants being the most strongly affected.

Influence of the Testa on Seed Dormancy, Germination, and Longevity in Arabidopsis

Bordered pits are cavities in the lignified cell walls of xylem conduits (vessels and tracheids) that are essential components in the water-transport system of higher plants. The pit membrane, which lies in the center of each pit, allows water to pass between xylem conduits but limits the spread of embolism and vascular pathogens in the xylem. Averaged across a wide range of species, pits account for > 50% of total xylem hydraulic resistance, indicating that they are an important factor in the overall hydraulic efficiency of plants. The structure of pits varies dramatically across species, with large differences evident in the porosity and thickness of pit membranes. Because greater porosity reduces hydraulic resistance but increases vulnerability to embolism, differences in pit structure are expected to correlate with trade-offs between efficiency and safety of water transport. However, trade-offs in hydraulic function are influenced both by pit-level differences in structure (e.g. average porosity of pit membranes) and by tissue-level changes in conduit allometry (average length, diameter) and the total surface area of pit membranes that connects vessels. In this review we address the impact of variation in pit structure on water transport in plants from the level of individual pits to the whole plant.

Structure and function of bordered pits: new discoveries and impacts on whole-plant hydraulic function

Differential staining of paraffin embedded plant material is accomplished without removing the paraffin. Material fixed in 3% glutaraldehyde in 0.02 M phosphate buffer is dehydrated, embedded, sectioned, and mounted on glass slides using conventional methods. The slides are placed in 0.05% toluidine blue O in distilled water for 2–30 min, rinsed in water for 1 min, and allowed to air dry. Paraffin is removed with 2 changes of xylene and the cover slip mounted with resin. Lignified tissue, suberized tissue, and some tannins are stained blue-green, while nonlignified walls are stained red-purple. An advantage of the method is the short time required for staining and mounting. Also, critical counterstaining is not required.

Simple method for differential staining of paraffin embedded plant material using toluidine blue O

An optical brightener Calcofluor White M2R New has been used to stain cell walls of higher plants. It can he used either as a vital stain for intact plants or for hand sections and plastic-embedded...

The Use of an Optical Brightener in the Study of Plant Structure

1.

The polychromatic staining of plant cell walls by toluidine blue O is described and illustrated.




2.

The effects of various common fixatives and the effects of the pH of the staining solution are evaluated.




3.

Simple and rapid procedures are described for preparing stained temporary mounts of fresh material, or permanent mounts of embedded and sectioned material.




4.

The relationship between the polychromatic staining observed and the lignification of the walls is discussed.

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Polychromatic staining of plant cell walls by toluidine blue O

I,n pre~i,ou.s ~pape.r,s ( O ' B r i e n an, d T , h i , m a n n 1965; T h i m a n n and O ' B r i e n 1965) ~the h,i:s.to.l, ogy of the eoleop,tiIe a p e x has been desc r ibed a n d i l lus t ra ted in s.ome ,detail. I't was ,shown t.ha,t the a p e x e,onsist,s of th ree ti~ssue:s: eipi, derm.is (.inner a n d outer) , va,scular sys,te~m, a n d p a r e n c h y m a . T h e e.el}s of the ~arenehyLma range b e t w e e n ,tw.o ,extremes. O n tfhe one hand , the cells nea res t 4he o,uter epi,derm:its ,o.n ,the p M o e m side .of the va's.eular bund les conta:in plast~ds which t u r n q.ud~te g reen .in t.he ~ig,ht. O n the o the r hand , .the pa renehy ,ma o.f the a v a s c u l a r r (w,hieh ,clo,s.e,s ,the eoleo.ptd~e) and the cells nea r e r ,the ~i.n~ne.r .epidermis f,a:il t.o Jd.ev.el,o~p a n y ap~preeiabl.e gr.ee~ p i g m e n t in the ~i~ht. The re,st .of the ~parenehy~m eel~Ls lie b.etween ~he,se two extrem,es, and it i,s ~el,e.ar t,hat ,in ~he s.ho~f,t o,f the eol,eoptile the c a p a c i t y to ' turn g reen show, s a ,marked r ad i a l g r a d i e n t t.ow,ar, ds the outside. A l though ,par,enehyma .eell,s .e,o~nst~,tute the b u l k ,of ,the l iv ing tis,s,ues of hi,gher .plant,s, s.urpr.i.sdrrg.ly l!i,ttle d a t a has b,een p u b l i s h e d on ' their fine s t ruc ture . S,u.eh infor,mat,i,an o~s .~her.e ,is co,m,es larg, e ly fr,o~m eell,s .of the eoleo,ptile. T,hu,s, A r r i g o n i and R o ~s .s ~i (,1962; 1964,) ,make b r i e f Inent ion of {he parenehy ,ma cel.Ls .but thei'r w o r k i,s concerned p r i m a r i l y w i t h the va scu l a r .spstem. W a r ,d r o O and F o s :t ,e r (1964) h a v e ,stud!i,ed 'the p a renehy.ma and ep:idermds .o,f y,o,ung e,o.leoptiles ,in .mater ia l f ixed ~n per~mangana te , whi le T ,h .o r n ,t o n arid T h i m a n n (19,64,) and C r o n s h a w (1964) h a v e b o t h r e p o r t e d on the crystal-e,onta~ining bo,dd.es ,o,f 4.hese e,ell~s in the o.at eo.leoptile. The wal'l~s of t:his ,tissue h a v e been s tud ied more e x t e n s i v e l y

Observations on the fine structure of the oat coleoptile

The cambium is t.hc lateral meristem that produces secondary xy lem and phloem in the axes and appendages of pract ica l ly all dicotyledons and gymnosperms. Research on cambium has followed several lines. A good deal of attention has been given \"to the s t ructure .of the cambium with emphasis on the divisions i n , and interconversions among, its component cells-the lustform and ray .initials (see reviews by B a n n a n 1955, 1962, E s a u 1965, chap. 6, S r i v a s t a v a 1964). Another impor tan t line of research has concerned itself with the dormancy ef cambium in winter and its reacfiraft.on in spring in tempera te climates. Hormones, ,such as auxin and giberellin, have been implicated, as well as day length and tempera ture (see reviews by L a r s . o n 1962, W a r e i n g et al. 1964, W . i l c o x 1962, W o r t 1962). Still other studies have deal t with the biochemical and morphogenetical factors involved in the differentiation of xy lem a n d phloem elements. Some of these, concerned with the changes in cell-wall constituents, have yielded encouraging results (see reviews by N o r t h c o t e 1963, S t e w a r t 1957, W o r t 1962). Others, based on tissue culture (see G a u t h e r e t 19'59) have been mostly unsuccessful, because the cambial cells in culture do not divide in the orderly manner typica l of their behavior in the intact plant ; instead they give ris.e to callus in which t racheary and phloem elements may be formed subsequently. The relevance of these

On the ultrastructure of cambium and its vascular derivatives

A n earl ier p a p e r (S r i v a ~ it a v ,a a n d O 'B 9 i e ~ 1966, P a r t I) ,described ~h,e ,s,tr:uct:ur:e o.f ,the .eamib,ial ~i~nit'iais in .the w'inter 'and ,s~uananer an~nth.s. T~he presen t :paper ,de,s,eri'bes the eh,ar~g,es in ~the ,cell :pr~f,o,pl,a,st which ~ e e o m p a n y ,differentiation .of t~he ,seieo,ndary iphlo, ean e~em,en:t,s. N'umer,o,u:s pape.r,s h a v e ,a, ppear,ed ~in recent yea~s .on ~th~e s t ruc tu re ,of :sieve eleanmlt~s, b.ased 'both m~ li.glh,t a n d e lec t ron mieroseopy. Ex:telrs~ive reviews of ~t]l'i~s, li,t.er,a~ture ~are ava.ilable (K o 1 '1 an a n n 1966, K o 1:1 an a n n an,cl .S ,e h urn ,a.e .h ,e r 19,66, E n ~g :1 e an la ,n 1965 a, b., E ~s a u and C h e a ,d 1 .e 1965) a n d ~t i.s no t necessary to d.uplie.a~e those effbr't,s .here. V e r y few ,tree s,p.eeies have been s tud ied : Larix (H u b 'e r arrd L i ,e s e 1963), Metas.equo.ia (K ,o. 11 an a n n and .S,e h,u In a e h.e x 19,5,6., and earliier' Faperls) a n d Tilia (E v.e r:t ,and M u r an a ,n .i !s 1'9'65). A s t u d y ~of 'the va.szu~ar ~tii~ssues ,i,n ,tr, ee,s pre,sent;s spec ia l pl~ob~eans o f fixat,ion a.n~d em'be, danent 'b~f i~t Eils .parlt~ieularly rewar, cli,ng beeau.se ~the ~s't.ages of ,d,ifferent:i,a:t4o,n ~of var,i.o.u,s. ,cell .ty,pe,s ,are: ~sharply e'ontra,s.te~cl wi:t!h :the rel.atively u,n,d;ifferien,~ia~fed ~ta.te .of ~the eam'b.i~al ini,t'i~als (see P a r t I). I n addi t ion , conifers have points of .special interes,t. Two types o,f pa ren ehyma cells can be d is t inguished in t,hese p lan t s : cells wh.ieh store s'tareh, phenol ic eompoun&s, or crystals , and cells which .do not aeeuanulate these p roduc t s bu t show a spec ia l physi.ologieal rel.ationship wi th the sieve elements , the so-called a~bulninous eells (S t r a s b u r g e r 189.1, p. 56, A b b e

On the ultrastructure of cambium and its vascular derivatives: II. Secondary phloem ofPinusstrobus L.

In the course of detailed investigations into the anatomy o[ the oat coleoptile, an unusual structure, having the nature of multivesicular elements, was ~b,served i,n the o,uter wall of the outer epidermal eel,ls. Although the differentially-thickened walls of this tissue have been well studied by H e y n t935, W u h r m a n n M e y e r f959, M i i h l e t h a l e r 1950, $ e t t e r f i e l d 1957, B a y l , e y etal. 1 9 5 ? , S e t t e r [ i e l d and B a y l e y 1958, 1959, G o r h a m and C o l v i n 19'57, B i i h m e r f958, none of these workers has described or illustrated the elements reported here.

T. P. O'Brien

Papers

Polychromatic staining of plant cell walls by toluidine blue O

Observations on the fine structure of the oat coleoptile

On the ultrastructure of cambium and its vascular derivatives

On the ultrastructure of cambium and its vascular derivatives: II. Secondary phloem ofPinusstrobus L.

Note on an unusual structure in the outer epidermal wall of the Avena coleoptile