DISPERSALOF

DIASPORESSUBMITTED BY:

AMANDEEPRAMANPREET

HARDEEP

SUBMITTED TO:

DR. SUNITA KAPILA

INTRODUCTIONDIASPORES-They are propagative parts of bryophytes that are capable of giving rise to a new individual . They include speacialised asexual structures like gemmae ,tubers, bulbils, fragile branches andleaves. These are often larger than spores and have higher germination rate.

VEGETATIVE PROPAGULESMany bryophytes produce vegetative propagules i.e gemmae.The gemmae may be filamentous, spindle shaped ,globular, discoid etc.Gemmae may be produced as outgrowth from some part of the gametophyte,in which case they are called exogenous gemmae.By contrast endogenous gemmae are formed within the gametophyte. Exogenous gemmae are attached to the gametophyte during their development but their attachment weakens as the gemmae matures,allowing the mature

EXOGENOUS GEMMAE IN MARCHANTIA

ENDOGENOUS GEMMAE in lophzia capitata

gemmae to be broken off fair easily .Endogenous gemmae are released by the breakdown of sorrounding cells. The great majority of bryophytes that produce exogenous gemmae do not do so in speacialised structures.Instead gemmae are most produce simply as outgrowth from some part of gametophyte thalli,stems,leaves,rhizoids depending on species. Exogenous gemmae are produced on the rhizoids of over 100 moss species.No liverwort or hornwort produce rhizoidal gemmae.

FOUR ABOVEGROUND TYPES OF PROPAGULES ARE:

1.Deciduous shoot apices results from an area weakened by a cleavage in the cell walls.These often already have rhizoidal initials at their basal parts.For example:BRYUM ARGENTEUM and CAMPYLOPUS JAPONICUS.Caducous branchlets seem like deciduous shoot apices,except that they are branch like structures with minute leaves & are attached to the parent plant by one celled stalk.

DECIDUOUS APICES IN BRYUM ARGENTEUM

2. Flagella are slender branches with reduced leaves and occur in the axil of upper leaves. The basal portion is multicellular,thus separating them from caducous branchlets.3.Bulbils usually occur on one-celled,short stalks and have what appear to partially developed leaves.Some are round and bulb like,others are thread like. They are common in POHLIA.4.Rhizoidal tubers occur on the rhizoids and are usually fi lamentous,branched or spherical and have diverse origin. They occur in species of BRYUM, POHLIA,and FISSIDENS.

BULBILS OF POHLIA

ANNOTINA

RHIZOIDAL TUBERS OF

BRYUM

VARIOUS AGENCIESOF

SPORE DISPERSAL

1.ANIMAL DISPERSALSpores adapted for animal dispersal are sticky and elliptical ,as in Splachaceae (dung mosses) these being dispersed by flies,beetles,slugs. Spider mites eat the gemmae of OCTOBLEPHARUM ALBIDUM. It is possible that some of these gemmae will get trapped among the hairs on the legs, thus getting transported by the mite.

SPIDER MITE FEEDING ON GEMMAE OF

OCTOBLEPHARUMALBIDUM

GEMMAE OF SCHISTOSTEG

APENNATA

2.WATER DISPERSAL*Schuster (1966) considers the dispersal of RICCIA and RICCIOCARPOUS by mud & water to be very frequent. They typically grow at margins of rivers and streams in the flood plains, where their spores mature in spring or in late summer and fall when flooding is common. *NOTOTHYLAS genus of hornworts is also likely to be dispersed in this way.*Aquatic mosses most likely primarily depend on water for dispersal.In winter aquatic mosses can get frozen in the ice.

When the ice breaks up, chunks may carry number of fragments downstream where some may become impinged on similar substrata*The best known method is the gemma cup or splash cup. Several bryophytes have specialised cups where the gemmae are produced and from which they are dispersed by raindrops.The splash cup mechanism seems to be engineered to maximise the distance its contents can splash ,thus forming an effective dispersal mechanism with the help of raindrops.

3.WIND DISPERSALMost bryophytes rely on wind for

spore dispersal. The vast majority of spores, typically with diameter 5-6 micrometers. For example,the moss genus ARCHIDIUM with spores diameter mostly in the range of 100-200 micrometer except A.denteri with diaspores of 50 micrometer. So ARCHIDIUM spores are too heavy for wind dispersal . Small spores can be carried to considerable distance by the wind.

MECHANISM OF SPORE DISPERSAL INBRYOPHYTESPOP GUN MECHANISM : In this mechanism

as the sporangia dries out , it shrinks in diameter and the columella collapse and is replaced by air space. The shrinking capsule place the air under considerable pressure. This pressure against operculum force it to be thrown off violently, unzipping the annulus ring and the spores are shot in the air with a sound which can be heard at a distance . For example- SPHAGNUM.

CENSOR OR SALT MECHANISM: IN this mechanism the apex of the columella is expanded to form epiphragm that nearly closes the capsule mouth . The margins of the epiphragm are attached to the inner tips of peristome teeth that arched over the epiphagm . Between each of the teeth and point of attachment of the margins of the epiphragm are tiny gaps and through the holes that the spores are ejected . For example : POLYTRICHUM.