Light induced electron spin polarization is an important consequence of charge separation in the primary photoreactions of photosynthesis.The informations on the structure and constituent of the primary photoreactions and their interaction could be obtained. In this paper

P

-700

+

and

A

1

-centers were studied in PSI of the intact soybean leaves with ESR techniques and curve fits at room temperature. For ESR measurements

the leaves were irradiated with ultraviolet light(337.1nm) and cw He-Ne laser. When orientation of the intact soybean leaves was changed in the magnetic field

we observed the dependence of electron spin polarization on the orientation.Our choice of the leaves for this study was based on the current model of the PSI reaction center organization

which may be represented as P-700

A

1

XFd

B

Fd

A

. According to the radical pair theory

we could write an approximate spin Hamiltonian of

P

-700

+

and A

1

-radical pair as

H=β

H

0

·((g

D

·S

D

+g

D

·S

A

)-J(2S

D

·S

A

+1/2)+ΣA

i

(D)

I

i

(D)

·S

D

+ΣA

i

(A)

I

i

(A)

S

A

and the experimental ESR intensity

I

p-700

+of

P-700

+as a function of field position H is given by

I

P-700

+(H)=Σ-(

p

i

)e(H-H

i

)

2

/δ

2

.