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T O T IP O T E N C Y A N D M O R P HO G E N E S IS OF P L A N T C E L L S

IN V I T R O

HISTOLOGICALANDULTRAS TR UCTURALASSAYOFSOMATIC

EMBRYOS

CITRUS SINENSIS CV.

TAROCCOUSINGFORTHEIR

QUALlTATIVEEVALUATION

V.N. Serebryakova, N.A.Moisseeva, L.Nardi*. P.Trionfeui Nisini*, S.Lucretti*

Institute o f Plant Physiology RussianAcademy o fSciences. Moscow127276,

Botanicheskaja ul, 35;

*ENEAC.R. Casaccia,Dip. INNOVAZIONE, Div. BiotecnologieedAgticoltura,

ViaAnguiliai ese. 301, 00060 S.M. di Galeria, Roma, Italy

Current literature on somatic embryogenesis in Citrus species is available

but no study has been undertaken to examine the whole sequence of

embryogenesis

in vitro,

i.e., globular, heart, torpedo and cotyledonary stage

of development. We have managed to elaborate appropriate culture conditions

allowing to sustain a high frequency of transition of selected cultures reaching

up to 80% for every individual step along the morphogenetic row. The present

microscopic assay has been mainly focused on histodifferentiation and

storage product deposition in order to assess morphological organization of

somatic embryos at every developmental stage. The general pattern of

histodifferentiation has kept the main features of a zygotic embryo. All the

tissues that are typical fo r a zygotic embryo, i.e., protoderm, ground tissue,

and procambium, were clearly identified at appropriate stage of development.

Besides there was revealed size-dependent control fo r protoderm

differentiation on globular embryo level. Thus, well-developed protoderm was

found only in the case of embryos the size of which varied between 1

,8x105

and 4,2x106

Globular embryos having a smaller size did not possess

discernible superficial layer of ceils. In contrast, the increase in the embryo

size above superior limit was linked to disruption of protoderm continuity

resulting from the commencement of repetitive embryogenesis. Protein and

lipid bodies and starch granules were found in ground tissue at heart and

torpedo stages. Only lipid bodies were numerously observed in cotyledon

cells. These features allow to predict functional similarity of somatic embryos

and argue in favor of their capacity to complete development.

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